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Computer Application and office automation
Contents;-
Unit – I
01-31
Introduction to computers – classification of digital computer systemAnatomy of a digital computer system – auxiliary storage sevices - input devices – output devices.
Unit – II
32-49
Introduction to computer software – oprating system – Programming languages – general software features and trends Data processing – Computer network.
Unit –III
50-62
COMMUNICATION SYSTEM
Unit – IV
63-78
MS Office acess
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UNIT-I INTRODUCTION TO COMPUTERS INTRODUCTION
A computer is a programmable machine. The two principal characteristics of a computer are : •
It responds to a specific set of instructions in a well-defined manner.
•
It can execute a prerecorded list of instructions (a program)
Modern computers are electronic and digital. The actual machinery – wires, transistors, and circuits – is called hardware; the instructions and data are called software. All general – purpose computers require the following hardware components: •
Central processing unit (CPU) The “heart” of the computer, the component that actually executes instructions.
•
Memory Enables a computer to store, at least temporarily, data and programs.
•
Input device Usually a keyboard or mouse, the input device is the conduit through which data and instructions enter a computer.
•
Output device A display screen, printer, or other such devices that lets you see what the computer has accomplished.
•
Mass storage device Allows a computer to permanently retain large amounts of data. Common mass storage devices include disk drives and tape drives.
In addition to these components, many others make it possible for the basic components of a computer to work together efficiently. For example, every computer requires a bus that transmits data from one part of the computer to another.
TYPES OF COMPUTERS Computers can be classified by their size and power as follows: •
Personal computer A small, single – user computer based on a microprocessor. In addition to the microprocessor, a personal computer has a keyboard for entering data, a monitor for displaying information, and a storage device for saving data.
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Workstation A powerful, single-user computer. A workstation is like a personal computer, but it has a more powerful microprocessor and a higher-quality monitor.
•
Minicomputer A multi-user computer capable of supporting 10 to hundreds of users simultaneously.
•
Mainframe A powerful multi-user computer capable of supporting many hundreds of users simultaneously.
•
Supercomputer An extremely fast computer that can perform hundreds of millions of instructions per second.
CLASSIFICATION OF DIGITAL COMPUTER SYSTEMS INTRODUCTION Computer
systems
are
classified
as
Microcomputers,
Minicomputers,
Mainframes and Supercomputers.
MICROCOMPUTERS The most familiar kind of computer is the microcomputer. In the past, microcomputers have been considered to be of two types – Personal Computers and Workstations. Personal Computers (PCs) PCs were desktop or portable machines .These machines ran comparatively easy – to – use applications software such as the word processors, spreadsheets, etc. They were usually easier to use and more affordable than workstations. However, they had less sophisticated video display screens, operating systems and networking capabilities. They did not have the processing power that workstations did. Examples of personal computers are Acer’s Aspire, Compaq Presario, etc.
Workstations Workstations expensive, powerful machines used by engineers, scientists, and other professionals who processed a lot of data. Workstations use high-resolution colour graphics and operating systems such as UNIX that permitted multitasking. Workstations also use powerful networking links to other computers. The most significant distinguishing factor, however, is the powerful processor, which could churn out results
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much faster than the PCs. The more powerful workstations are called supermicros. Examples of well-known workstations are those made by Sun, Apollo, Hewlett-Packard, NeXT and IBM. PCs are now as powerful as many of those used in workstations. More powerful microprocessors and increased graphics and communications capabilities now let end users run software that previously ran only on more powerful machines. Portable Computers Personal computing market is seeing the miniaturization phenomena. Computers are becoming smaller yet more powerful. There are three categories of portable computers: Laptops or Notebook PCs, Subnotebooks and Personal Digital Assistants. Laptops / Notebooks : Laptops may be either AC-powered, battery-powered, or both. These computers are ideal for users who have to work away from their offices .The user of these computers might be an executive on the move, a student, a journalist, a salesperson, etc. Subnotebooks: Subnotebooks are for frequent flyers and life–on-the-road professionals. Subnotebook users give up a full display screen and keyboard in exchange for less weight. These computers fit easily into any briefcase. They typically have an external floppy disk drive and monochrome monitor, although of late colour models are available. An example of a colour sub notebooks is Toshiba Protégé. Personal Digital Assistants (PDAs) PDAs are much smaller than the sub notebooks. They combine pen input, writing recognition, personal organization tools, and communication capabilities in a very small package. Typical users are executives, businessmen, etc. who use these machines for their day-to-day activities – scheduling, organization, etc. An example PDA is Apple’s Newton. MINICOMPUTERS Minicomputers, also known as mid range computers. They were used to control machines in a manufacturing unit. They are widely used as general – purpose computers. The more powerful minicomputer models are called superminis. The increasing power of microcomputer gives minutes. One of the popular minicomputer systems is the VAX made by Digital Equipment Corporation.
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Minicomputers work well in what are known as Distributed Data Processing (DDP). That is, a company’s processing power is decentralized, or distributed across different computers. An example of such a computer architecture is the Client/Server model, in which end users can process at their own microcomputers. End users can also access and share the resources of the server, which usually is a minicomputer. For example, an executive could use the server to search the company’s centralized database and retrieve selected data. He / she could then use a spreadsheet on his/her microcomputer to analyze the data.
MAINFRAMES Mainframe computers can process several million – program instructions per second. Large organizations rely on these room-size systems to handle large programs with lots of data. Mainframes are mainly used by insurance companies, banks, airline and railway reservation systems, etc. An advanced mainframe made by IBM is S/390. SUPERCOMPUTERS Supercomputers are the fastest calculating devices. A desktop microcomputer processes data and instructions in millionths of a second, or microseconds. A supercomputer, by contrast, can operate at speeds measured in nanoseconds and even in picoseconds. One thousand to one million times as fast as microcomputers. Most supercomputers are used by government agencies. These machines are for applications requiring very large programs and huge amounts of data that must be processed quickly. Examples of such task are weather forecasting, oil exploration, weapons research, and large-scale simulation. The chief difference between a supercomputer and a mainframe is that a supercomputer channels all its power into executing a few programs as fast as possible, whereas a mainframe uses its power to execute many programs concurrently. Supercomputers use a technology called massively parallel processing. These supercomputers consist of thousands of integrated microprocessors. One massively parallel computer built by Intel Corporation is capable of performing 8.6 billion mathematical calculations per second.
NETWORK COMPUTERS Network computers are computers with minimal memory, disk storage and processor power designed to connect to a network, especially the Internet .Network
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computers is that many users who are connected to a network. Network computers designed to connect to the internet are sometimes called internet boxes, Net PCs and Internet appliances. ANATOMY OF A DIGITAL COMPUTER
FUNCTIONS AND COMPONENTS OF A COMPUTER To function properly, the computer needs both hardware and software. Hardware consists of the mechanical and electronic devices. The software consists of programs, the operating systems and the data that reside in the memory and storage devices. A computer does mainly the following four functions: •
Receive input – Accept information from outside through various input devices like the keyboard, mouse, etc.
•
Process information – perform arithmetic or logical operations on the information.
•
Produce output – Communicate information to the outside world through output devices like monitor, printer, etc.
•
Store information – Store the information in storage devices like hard disk, floppy disks, etc.
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Computer hardware falls into two categories: processing hardware, which consists of the central processing unit (CPU), and the peripheral devices. CENTRAL PROCESSING UNIT (CPU) The part of the computer that executes program instructions is known as the processor or central processing unit (CPU). The CPU has two parts – the control unit and the arithmetic – logic unit (ALU). Control unit The control unit tells the rest of the computer system how to carry out a program’s instructions. It directs the movement of electronic signals between memory – which temporarily holds data, instructions and processed information – and the ALU. It also directs these control signals between the CPU and input/ output devices. Arithmetic – Logic Unit (ALU) Arithmetic Logic Unit, usually called the ALU, performs two types of operations – arithmetic and logical.
Arithmetic operations are the fundamental mathematical
operations consisting of addition, subtraction, multiplication and division.
Logical
operations consist of comparisons. That is, two pieces of data are compared to see whether one is equal to., less than, or greater than the other. MEMORY Memory – also known as the primary storage or main memory – is a part of the microcomputer that holds data for processing, instructions for processing the data (the program) and information. Part of the contents of the memory is held only temporarily, that is, it is stored only as long as the microcomputer is turned on. When you turn the machine off, the contents are lost.
The capacity of the memory to hold data and
program instructions varies in different computers hold approximately 6,40,000 characters of data or instructions only. But modern microcomputers can hold millions, even billions of characters in their memory. REGISTERS Computers also have several additional storage locations called registers. These appear in the control unit and ALU and make processing more efficient. Registers areas hold data and instructions temporarily during processing. They are parts of the control unit and ALU rather than the memory.
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ADDRESSES To locate the characters of data or instructions in the main memory, the computer stores them in locations known as addresses. A unique number designates each address. Addresses can be compared to post office mailboxes. Their numbers stay the same, but contents continuously change.
HOW THE CPU AND MEMORY WORK The various steps involved for multiplying two numbers is explained below: 1. The control unit recognizes that the programs has been loaded into memory. It begins to execute the first step in the program. 2. The program tells the user, “Enter 1st Number.” 3. The user types the number 10 on the keyboard. An electronic signal is sent to the CPU. 4. The control unit recognizes this signal and routes the signal to an address in memory – address 7. 5. After completing the above instruction, the next instruction tells user, “Enter 2nd Number.” 6. The user types the number 4 on the keyboard. An electronic signal is sent to the CPU. 7. The control unit recognizes this signal and routes it to memory address 8. 8. The next program instruction is executed – “Multiply 1st and 2nd Numbers.”
9. To execute this instruction, the control unit informs the ALU that two numbers are coming and the ALU is to multiply them. The control unit next sends to the ALU a copy of the contents of address 7(10) and address 8 (4). 10. ALU performs the multiplication: 10 X 4 = 40. 11. The control unit sends a copy of the multiplied result (40) back to memory, to address 9.
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12. The next program instruction is executed: “Print the Result.’ 13. To execute this instruction, the control unit sends the contents of the address 9(40) to the monitor. 14. Monitor displays the value 40. 15. Final instruction is executed: “End.” The program is complete.
INPUT DEVICES
INTRODUCTION An input device is any machine that feeds data into a computer. For example, a keyboard is an input device, whereas a display monitor is an output device.
Input
devices other than the keyboard are sometimes called alternate input devices. Mice, trackballs, and light pens are all alternate input devices. KEYBOARD Keyboard is an input device consisting of a set typewriter-like keys that enable you to enter data into a computer. Computer keyboards are similar to electric-typewriter keyboards but contain additional keys.
The keys on computer keyboards are often
classified as follows: •
Alphanumeric keys – letters and numbers
•
Punctuation keys – comma, period, semicolon, and so on.
•
Special keys – function keys, control keys, arrow keys, caps Lock key, and so on.
There are actually three different PC keyboards: the original PC keyboard, with 84 keys; the AT keyboard, also with 84 keys; and the enhanced keyboard, with 101 keys. In addition to these keys, IBM keyboards contain the following keys: Page UP, Page Down, Home, End, Insert, Pause, Num Lock, Scroll Lock, Break, Caps Lock, Print Screen. MOUSE Mouse is a device that controls the movement of the cursor or pointer on a display screen. A mouse is a small object you can roll along a hard, flat surface. As you move the mouse, the pointer on the display screen moves in the same direction. Mice contain at least one button and sometimes as many as three, which have different functions depending on what program is running.
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In particular, the mouse is important for graphical user interfaces because you can simply point to options and objects and click a mouse button. Such applications are often called point- and – click programs.
The mouse is also useful for graphics
programs that allow you to draw pictures by using the mouse like a pen, pencil, or paintbrush. Types of Mice There are three basic of Mice. Mechanical Has a rubber or metal ball on its underside that can roll in all directions. Mechanical sensors within the mouse detect the direction the ball is rolling and move the screen pointer accordingly. Optomechanical
Same as a mechanical mouse, but uses optical sensors to
detect motion of the ball. Optical Uses a laser to detect the mouse’s movement. You must move the mouse along a special mat with a grid so that the optical mechanism has a frame of reference. Optical mice have no mechanical moving parts. They respond more quickly and precisely than mechanical and optomechanical mice, but they are also more expensive. Connections Mice connect to PCs in one of three ways: •
Serial mice connect directly to an RS-232C serial port or a PS/2 port. This is the simplest type of connection.
•
Bus mice connect to the bus through an interface card. This is somewhat more complicated because you need to configure and install an expansion board.
•
Cordless mice aren’t physically connected at all. Instead they rely on infrared or radio waves to communicate with the computer.
Mouse pad Mouse pad is a pad over which you can move a mouse. TRACKBALL Trackball is another pointing device. Essentially, a trackball is a mouse lying on its back. To move the pointer, you rotate the ball with your thumb, your fingers, or the palm of your hand. There are usually one to three buttons next to the ball, which you use just like mouse buttons. The advantage of trackballs over mice is that the trackball is stationary so it does not require much space to use it. In addition, you can place a trackball on any type of
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surface, including your lap. For both these reasons, trackballs are popular pointing devices for portable computers. JOYSTICK A lever that moves in all directions and controls the movement of a pointer or some other display symbols. A joystick is similar to a mouse, except that with a mouse cursor stops moving as soon as you stop moving the mouse.
With a joystick, the pointer continues moving in the direction the joystick is pointing. To stop the pointer, you must return the joystick to its upright position. Joystick are used mostly for computer games, but they are also used occasionally for CAD/CAM systems and other applications. DIGITIZING TABLET This is an input device that enables You to enter drawings and sketches into a computer. A digitizing tablet consist of an electronic tablet and a cursor or pen. A cursor (also called a puck) is similar to a mouse, except that it has window with crosshairs for pinpoint placement and it can have as any as 16 buttons A pen (also called a stylus) which looks like a simple ballpoint pen but uses an electronic head instead of ink. The tablet contains electronic that enable it to detect movement of the cursor or pen and translate the movements into digital signals that it sends to the computer. Digitizing tablet are also called digitizers, graphics tablets, touch tablets, or simply tablets. SCANNERS Scanner is an input device that can read text or illustrations printed on paper and translate the information into a form that the computer can use. A scanner works by digitizing an image – dividing it into a grid of boxes and representing each box with either a zero or a one, depending on whether the box is filled in. The resulting matrix of bits, called a bit map, can then be stored in a file, displayed on a screen, and manipulated by programs. Optical scanners do not distinguish text from illustrations; they represent all images as bit maps. Therefore, you cannot directly edit text that has been scanned. To edit text read by an optical scanner, you need an optical character recognition (OCR)
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system to translate the image into ASCII characters. Most optical scanners sold today come with OCR packages. Scanners differ from one another in the following respects: Scanning technology Most scanners use charge – coupled device (CCD) arrays, which consists of tightly packed rows of light receptors that can detect variations in light intensity and frequency. The quality of the CCD array is probably the single most important factor affecting the quality of the scanner. Industry – strength drum scanners use a different technology that relies on a photomultiplier tube (PMT) but this type of scanner is much more expensive than the more common CCD – based scanners. Resolution The denser the bit map, the higher the resolution.
Typically,
scanners support resolutions from 72 to 600 dots per inch (dpi). Bit depth The number of bits used to represent each pixel. The greater the bit depth, the more colors or grayscales can be represented. For example, a 24-bit color scanner can represent 2 to the 24th power (16.7 million) colors. Note, however, that a large color range is useless if the CCD arrays are capable of detecting only a small number of distinct colors. Size and shape Some scanners are small hand-held devices that you move across the paper.
These hand- held scanners are often called half-page scanners
,which are adequate for small pictures and photos, but they are difficult to use if you need to scan an entire page of text or graphics. Larger scanners include machines into which you can feed sheets of paper. These are called sheet-fed scanners. Sheet-fed scanners are excellent for loose sheets of paper, but they are unable to handle bound documents.
A second type of large scanner, called a flatbed scanner, is like a
photocopy machine. It consist of a board on which you lay books, magazines, and other documents that you want to scan. DIGITAL CAMERA Images can be input into a computer using a digital camera. These images can then be manipulated in many ways using the various imaging tools available. The digital camera takes a still photograph, stores it, and then sends it as digital input into the computer. The images are then stored as digital files. MAGNETIC INK CHARACTER RECOGNITION (MICR) Magnetic Ink Character Recognition (MICR) allows the computer to recognize characters printed using magnetic ink. MICR is a direct-entry method used in banks. This technology is used to automatically read those frustrating – looking numbers on the
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bottom of the cheque. A special –purpose machine known as a reader/sorter reads characters made of ink containing magnetized particles. A related technology is the magnetic strip, used on the back of credit cards and bank debit cards, that allows readers such as Automated Teller Machines (ATMs) to read account information and facilitate monetary transactions. Another example of magnetic strip technology is in ID cards, which can be used for a variety of functions from attendance monitoring to restricting access to specific locations. OPTICAL CHARACTER RECOGNITION (OCR) Often abbreviated OCR, optical character recognition refers to the branch of computer science that involves reading text from paper and translating the images into a form that the computer can manipulate (for example, into ASCII codes).
An OCR
system enables you to take a book or a magazine article and feed it directly into an electronic computer file. All OCR systems include an optical scanner for reading text, and sophisticated software for analyzing images. Most OCR systems use a combination of hardware (specialized circuit boards) and software to recognize characters, although some inexpensive systems do it entirely through software. Advanced OCR systems can read text in a large variety of fonts, but they still have difficulty with handwritten text. OPTICAL MARK RECOGNITIO0N (OMR) Optical Mark Recognition (OMR) also called mark sensing is a technology where an OMR device senses the presence or absence of a mark, such as a pencil mark. OMR is used in tests such as aptitude tests. BAR CODE READER You are probably familiar with the bar code readers in supermarkets, bookshops, etc. Bar code readers are photoelectric scanners that read the bar codes, or vertical zebra striped marks, printed on product containers.
Supermarkets use a bar code
system called the Universal Product Code (UPC). The bar code identifies the product to the supermarket’s computer, which has a description and the latest price of the product. The computer automatically tells the POS (Point Of Sales) terminal what the price is. SPEECH INPUT DEVICES Speech or voice input devices convert a person’s speech into digital form. These input devices, when combined with appropriate software, form voice recognition
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These systems enable users to operate microcomputers using voice
commands. Some of these systems must be ‘trained ’ to the particular user’s voice. This is done by his/her spoken words to patterns previously stored in the computer. More advanced systems that can recognize the same word spoken by many different people have been developed. However, until recently the list of words has been limited. A newly developed voice recognition system like IBM Voice Type identifies more than 30,000 words and adapts to individual voices. There are even systems that will translate from one language to another, such as from English Japanese. There are two types of voice recognition systems: •
Continuous Speech
•
Discrete – Word
Continuous Speech Continuous speech recognition systems are used to control a microcomputer’s operations and to issue commands to special application programs. For example, rather than using the keyword to save a spreadsheet file, the user could simply say “Save the file”.
Two popular systems are Apple Computer’s Plain Talk and IBM’s continuous
speech series. Discrete – word A common activity in business is preparing memos and other written documents. Discrete – word recognition systems allow users to dictate directly into a microcomputer using a microphone. The microcomputer stores the memo in a word processing file where it can be revised later or directly printed out. IBM Voice Type Simply Speaking is an example. TOUCH SCREEN Touch screen is a type of display screen that has a touch-sensitive transparent panel covering the screen. Instead of using a pointing device such as a mouse or light pen, you can use your finger to point directly to objects on the screen. Although touch screens provide a natural interface for computer novices, they are unsatisfactory for most applications because the finger is such a relatively large object. It is impossible to point accurately to small areas of the screen. In addition, most users find touch-screens tiring to the arms after long use.
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TOUCH PAD A small, touch – sensitive pad used as a pointing device on some portable computers. By moving a finger or other object along the pad, you can move the pointer on the display screen. LIGHT PEN Light pen is an device that utilizes a light – sensitive detector select objects on a display screen. A light pen is similar to a mouse, expect that with a light pen you can move the pointer and select objects on the display screen by directly pointing to the objects with the pen.
OUTPUT DEVICES
INTRODUCTION Output is anything that comes out of a computer.
An output device is any
machine capable of representing information from a computer. Output devices include display screens, loudspeakers, printers, plotters, etc. MONITOR Monitor is another term for the display screen.
The term monitor, however,
usually refers to the entire box, whereas display screen can mean just the screen. CLASSIFICATION OF MONITORS – BASED ON COLOUR There are many ways to classify monitors. The most basic is in terms of colour capabilities, which separates monitors into three classes.
Monochrome Monochrome monitors actually display two colours, one for the background and one for the foreground. The colours can be black and white, green and black, or amber and black. and white, green and black, or amber and black. Gray – scale A gray – scale monitor is a special type of monochrome monitor capable of displaying different shades of gray. Colour Colour monitors can display anywhere from 256 to over 1 million different colours. Colour monitors are sometimes called RGB monitors because they accept
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three separate signals – red, green, and blue. All colour computer monitors are RGB monitors. An RGB monitor consists of a vacuum tube with three electron guns – one each for red , green, and blue at one end and the screen at the other end. The three electron
guns fire electrons at the screen, which contains a phosphorous coating.
When the electron beams excite the phosphors, they glow. Depending on which beam excites them, they glow red, green, or blue. Ideally, the three beams should converge for each point on the screen so that each pixel is a combination of the three colours. Colour and gray – scaling monitors are often classified by the number of bits they use to represent each pixel. For example, an 8- bit monitor each pixel with 8 bits. The more bits per pixel, the more colours and shades of gray the monitor can display.
CLASSIFICATION MONITORS – BASED ON SIGNALS: Another common way of classifying is in terms of the type of signal they accept; analog or digital. Digital Monitor A digital monitor accepts digital signals rather than analog signals. All monitors (except flat- panel displays) use CRT technology, which is essentially analog. The term digital, therefore, refers only to the type of input received from the video adapter. A digital monitor then translates the digital signals into analog signals that control the actual display. Although digital monitors are fast and produce clear images, they cannot display variable colours continuously. Consequently, only low-quality video standards such as MDA (Monochrome Display Adepter), CGA (Colour/Graphics Adapter), and EGA (Enhanced Graphics Adapter), specify digital signals. VGA (Video Graphics Array) and SVGA (Super VGA), on the other hand, require an analog monitor. Some monitors are capable of accepting either analog or digital signals. Analog Monitor This is the traditional type of colour display screen that has been used for years in televisions. In reality, all monitors based on CRT technology (that is, all monitors except flat- panel displays) are analog.
Some monitors, however, are called digital
monitors because they accept digital signals from the video adapter. EGA monitors, for example, must be digital because the EGA standard specifies digital signals. Digital
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monitors must nevertheless translate the signals into an analog form before displaying images. Some monitors can accept both digital and analog signals. Some monitors have fixed frequency, which means that they accept input at only one frequency. Another type of monitor, called a multiscanning monitor, automatically adjusts to the frequency of the signals being sent to it. This means that it can accept input from different types of video adapters.
Like fixed – frequency monitors,
multiscanning monitors accept TTL, analog, or both types of input. CHARACTERISTICS OF A MONITOR: Size The most important aspect of a monitor is its screen size.
Like televisions,
screen sizes are measured in diagonal inches, the distance from one corner to the opposite corner diagonally.
A
typical size for small VGA monitors is 14 inches.
Monitors that are 16 or more inches diagonally are often called full- page monitors. In addition to their size, monitors can be either portrait (height greater than width)
or
landscape (width greater than height). Larger landscape monitors can display two full pages, side by side. Resolution The resolution of a monitor indicates how densely the Pixel is short for Picture Element.
A pixel is a single
pixels
are
packed.
point in a graphic image.
Graphics monitors display pictures by dividing the display screen into thousands (or millions) of pixels, arranged in rows and columns. The number of bits used to represent each pixel determines how many colours or shades of gray can be displayed. For example an 8- bit colour monitor uses 8 bits for each pixel, making it possible to display 2 to the 8th power (256) different colours or shades of gray. On colour monitors, each pixel is actually composed of three dots – a red, a blue, and a green one.
The quality of a display monitor largely depends on its
resolution, how many pixels it can display, and how many bits are used to represent each pixel. VGA monitors display 640 by 480, or about 300,000 pixels. In contrast, SVGA monitors display 1,024 by 768, or nearly 800,000 pixels. Most modern monitors can display 1024 by 768 pixels, the SVGA standard. Some high – end models can display 1280 by 1024, or even 1600 by 1200.
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Bandwidth The amount of data that can be transmitted in a fixed amount of time. For digital devices, the bandwidth is usually expressed in bits or bytes per second (bps). For analog devices, the bandwidth is expressed in cycles per second, or Hertz (Hz).
Refresh Rate Display monitors must be refreshed many times per second. The refresh rate determines hoe many times per second the screen is to be refreshed (redrawn). The refresh rate for a monitor is measured in hertz (Hz) and is also called the vertical frequency or vertical refresh rate. The old standard for monitor refresh rates was 60 Hz, but a new standard developed by VESA sets the refresh rate at 75Hz for VGA and SVGA monitors. The faster the refresh rate, the less the monitor flickers. Interlaced or Non – interlaced Interlacing is a display technique that enables a monitor to provide more resolution in expensively. With interlacing monitors, the electron guns draw only half the horizontal lines with each pass (for example, all odd lines on one pass and all even lines on the next pass). Because an interlacing monitor refreshes only half the lines at one time, it can display twice as many lines per refresh cycle, giving it greater resolution. Another way of looking at it is that interlacing provides the same resolution as noninterlacing, but less expensively.
A shortcoming of interlacing is that the reaction time
is slower, so programs that depend on quick refresh rates (animation and video, for example), may experience flickering or streaking. Given two monitors that offer the same resolution, the non – interlacing one will generally be better. Dot – pitch A measurement that indicates the vertical distance between each pixel on a display screen.
Measured in millimeters, the dot pitch is one of the principal
characteristics that determine the quality of display monitors. The dot pitch of colour monitors for personal computers ranges from about 0.15 mm 0.30mm. Another term for dot pitch is phosphor pitch. Convergence Convergence refers to how sharply an individual colour pixel on a monitor appears. Each pixel is composed of three dots – a red, blue, and green one. If the dots are badly misconverged, the pixel will appear blurry.
All monitors have some
convergence errors, but they differ in degree.
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VIDEO STANDARDS There are a variety of video standards that define resolution and colours for displays. Support for a graphics standard is determined by both the monitor and the video adapter. The monitor must be able to show the resolution and colours defined by the standard, and the video adapter must be capable of transmitting the appropriate signals to the monitor. Listed here, in approximate order of increasing power and sophistication, are the more popular video standards for PCs. Note that many of these numbers represent only the minimums specified in the standards. Many suppliers of video adapters provide greater resolution and more colours. For more information, refer to the entries for the specific graphics systems given in table 9.1.
VGA Abbreviation of video graphics array, a graphics display system for PCs developed by IBM. VGA has become one of the de facto standards for PCs. In text mode, VGA systems provide a resolution of 720 by 400 pixels. In graphics mode, the resolution is either 640 by 480 (with 16 colours) or 320 by 200 (with 256 colours). The total palette of colours is 262,144.
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SVGA Short for Super VGA, a set of graphics standards designed to offered greater resolution than VGA. There are several varieties of SVGA, each providing a different resolution: •
800 by 600 pixels
•
1024 by 768 pixels
•
1280 by 1024 pixels
•
1600 by 1200 pixels
All SVGA standards support a palette of 16 million colours, but the number of colours that can be displayed simultaneously is limited by the amount of video memory installed in a system. 8514/A A high – resolution video standard for PCs developed by IBM in 1987. It was designed to extend the capabilities of VGA.
The 8514/A standard provides a
resolution of 1,024 by 768 pixels, which gives it about 2.5 times the pixels of VGA (640 by 480). Like VGA, 8514/A provides a palette of 262,000 colours, of which 256 can be displayed at one time. On monochrome displays, 8514/A provides 64 shades of gray. XGA Short for extended graphics array, a high – resolution graphics standard introduced by IBM in 1990. XGA was designed to replace the order 8514/A video standard. It provides the same resolutions (640 by 480 or 1024 by 768 pixels), but supports more simultaneous colours (65 thousand compared to 8514/A’s 256 colours). In addition, XGA allows monitors to be non – interlaced.
TI 34010 TI 34010 is a video standard from Texas Instruments that supports a resolution of 1,024 by 768. TI 34010 conforms to TI’s Graphics Architecture (TIGA ). Unlike IBM’s 8514/A, which supports the same resolution. TI 34010 is non – interlaced.
PRINTER Printer is a device that prints text or illustrations on paper and in many cases on transparencies and other media. There are many different types of printers. In terms of the technology utilized, printers fall into the following categories.
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Daisy – wheel Printer Daisy – wheel printers are a type of printer that produces letter- quality type.
A daisy – wheel printer works on the same principles as a ball – head
typewriter. The daisy wheel is a disk made of plastic or metal on which characters stand out in relief along the outer edge. To print a character, the printer rotates the disk until the desired letter is facing the paper. Then a hammer strikes the disk, forcing the character to hit an ink ribbon, leaving an impression of the character on the paper. You can change the daisy wheel to print different fonts. Daisy – wheel printers cannot print graphics, and in general they are noisy and slow, printing from 10 t about 75 characters per second. Dot – matrix Printer Dot – matrix printers create characters by striking pins against an ink ribbon.
Each pin makes a dot, and combinations of dots form characters and
illustrations. Dot- matrix printers are inexpensive and relatively fast, but they do not produce high – quality output. Dot – matrix printers vary in two important characteristics: •
Speed – Given in characters per second (cps), the speed can vary from about 50 to over 500 cps.
•
Print quality – Determined by the number of pins (the mechanisms that , print the dots), it can vary from 9 to 24. The best dot– matrix printers (24 pins) can produce near letter- quality type, although you can still see a difference if you look closely.
Ink – jet Printer Ink – jet printers work by sparing ionized ink at a sheet of paper. Magnetized plates in the ink’s path direct the ink onto the paper in the paper in the desired shapes.
Ink – jet printers are capable of producing high quality print
approaching that produced by laser printers.
A typical ink- jet printer provides a
resolution of 300 dots per inch. The price of ink – jet printers is lower than that of laser printers. However, they are also considerably slower. Another drawback of ink – jet printers is that they require a special type of ink that is apt to smudge on inexpensive copier paper. Laser Printer Laser printer utilizes a laser b4eam to produce an image on a drum. The light of the laser alters the electrical charge on the drum wherever it hits. The drum is
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then rolled through a reservoir of toner, which is picked up by the charged portions of the drum. Finally, the toner is transferred to the paper through a combination of heat and pressure. Because an entire page is transmitted to a drum before the toner is applied. Laser printers are sometimes called page printers. There are two other types of page printers that fall under the category of laser printers even though they do not use lasers at all. One uses an array of LEDs to expose the drum, and the other uses LCDs. Once the drum is charged, however, they both operate like a real laser printer.
One of the chief characteristics of laser printers is their resolution – how many dots per inch (dpi) they lay down. The available resolutions range from 300 dpi at the low end to 1,200 dpi at the high end. By comparison, offset printing usually prints at 1,200 or 2,400 dpi.
Some laser printers achieve higher resolutions with special
techniques known generally as resolution enhancement. In addition to the standard monochrome laser printer, which uses a single toner, there also exist colour laser printers that use four toners to print in full colour. Colour laser printers tend to be about five to ten times as expensive as their monochrome siblings. Laser printers produce very high – quality print and are capable of printing an almost unlimited variety of fonts. Most laser printers come with a basic set of fonts, called internal or resident fonts, but you can add additional fonts in one of two ways: •
Font cartridges – Laser printers have slots in which you can insert font cartridges, ROM boards on which fonts have been recorded. The advantage of font cartridges is that they use none of the printer’s memory.
•
Soft fonts – All laser printers come with a certain amount of RAM memory, and you can usually increase the amount of memory by adding memory boards in the printer’s expansion slots. You can then copy fonts from a disk to the printer’s RAM. This is called downloading fonts. A font that has been downloaded is often referred to as a soft font, to distinguish it from the hard fonts available on font cartridges. The more RAM a printer has, more fonts that can be downloaded at one time.
LCD & LED Printers Similar to a laser printer but uses liquid crystals or light – emitting diodes rather than a laser to produce an image on the drum.
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Line Printer Line printers are high speed printers capable of printing an entire line at one time. A fast line printer can print as many as 3,000 lines per minute.
The
disadvantages of line printers are that they can print only one font, they cannot print graphics, the print quality is low, and they are very noisy. Thermal printer Thermal printers are printers that produce images by pushing electrically heated pins against special heat- sensitive paper. Thermal printers are inexpensive and are used in most calculators and many fax machines. They produce low- quality print, and the paper tends to curl and fades after a few weeks or months. Printers are also classified according to the following characteristics: •
Quality of type – Type output produced by printers is said to be either letter quality (as good as a typewriter), near letter quality, or draft quality. Only daisy wheel, ink – jet, and laser printers produce letter- quality type. Some dot –matrix printers claim letter – quality print, but if you look closely, you can see the difference.
•
Speed – Measured in characters per second (cps) or pages per minute (ppm), the speed of printers varies widely.
Daisy – wheel printers tend to be the
slowest, printing about 30 cps. Line printers are fastest (up to 3,000 lines per minute). Dot – matrix printers can print up to 500 cps, and laser printers range from about 4 to 20 text pages per minute. •
Impact or non – impact – Impact printers include all printers that work by striking an ink ribbon. Daisy – wheel, dot – matrix, and line printers are impact printers. Non – impact printers include laser printers and ink – jet printers. The important difference between impact and non – impact printers is that impact printers are much noisier but are useful for making multiple copies like carbon copies.
•
Graphics – Some printers (daisy – wheel and line printers) can print only text. Other printers can print both text and graphics.
•
Fonts – Some printers, notably dot –matrix printers, are limited to one or a few fonts. In contrast, laser and ink – jet printers are capable of printing an almost unlimited variety of fonts. Daisy – wheel printers can also print different fonts, but you need to change the daisy wheel, making it difficult to mix fonts in the same document.
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PLOTTER Plotter is a device that draws pictures on paper based on commands from a computer. Plotters differ from printers in that they draw lines using a pen. As a result, they can produce continuous lines, whereas printers can only simulate lines by printing a closely spaced series of dots. Multicolour plotters use different – coloured pens to draw different colours. In general, poltters are considerably more expensive than printers. They are used in engineering applications where precision is mandatory.
SOUND CARDS & SPEAKERS An expansion board that enables a computer to manipulate and output sounds. Sound cards are necessary for nearly all CD-ROMs and have become commonplace on modern personal computers. Sound cards enable the computer to output sound through speakers connected to the board, to record sound input from a microphone connected to the computer, and ,manipulate sound stored on a disk. Nearly all sound cards support MIDI, a standard for representing music electronically. In addition, most sound cards are Sound Blaster – compatible, which means that they can process commands written for a Sound Blaster care, the de facto standard for PC sound. Sound cards use two basic methods to translate digital data into analog sounds: •
FM (Frequency Modulation) Synthesis mimics different musical instruments according to built – in formulas.
•
Wavetable Synthesis relies on recordings of actual instruments to produce sound. Wavetable synthesis produce more accurate sound, but is also more expensive.
3D Audio 3D audio is a technique for giving more depth to traditional stereo sound. Typically, 3D sound, or 3D audio, is produced by placing a device in a room with stereo speakers. The device dynamically analyzes the sound coming from the speakers and sends feedback to the sound system so that it can readjust the sound to give the impression that the speakers are further apart. 3D audio devices are particularly popular for improving computer audio where speakers tend to be small and close together. There are a number of 3D audio devices that attach to a computer’s sound card.
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AUXILIARY STORAGE DEVICES INTRODUCTION Auxiliary storage also known as auxiliary memory or secondary storage, is the memory that supplements the main storage. This is a long – term, non – volatile memory. The term non –volatile means it stores and retains the programs and data even after the computer is switched off. Unlike RAM which looses the contents when the computer is turned off, and ROM, to which it is not possible to add anything new, auxiliary storage devices allows the computer to record information semi – permanently, so it can be read later by the same computer or by another computer. Auxiliary storage devices are also useful in transferring data or programs from one computer to another. They also function as back – up devices which allows to back – up the valuable information that you are working on.
So even if by some accident your computer
crashes and the data in it is unrecoverable, you can restore it from your back – ups. The most common types of auxiliary storage devices are magnetic disks, floppy disks, hard disks, etc. There are two types of auxiliary storage devices. This classification is based on the type of data access: sequential and random. Based on the type of access they are called sequential – access media and random – media. In the case of sequential – access media, the data stored in the media can only be read in sequence and to get to a particular point on the media you have to go through all the preceding points. Magnetic tapes are examples of sequential access media. In contrast, disks are random access also called direct access media because a disk drive can access any point at random without passing through intervening points. Other examples of direct access media are magnetic disks, optical disks, zip disks etc. MAGNETIC TAPE Magnetic tape is a magnetically coated strip of plastic on which data can be encoded. Tapes for computers are similar to the tapes used to store music. Some personal computers, in fact, enable you to use normal cassette tapes. Storing data on tapes is considerably cheaper than storing data on disks. Tapes also have large storage capacities, ranging from a few hundred kilobytes to several gigabytes. Accessing data on tapes, however, is much slower than accessing data on disks. Tapes are sequential access media, which means that to get to a particular point on the tape, the tape must go through all the preceding points. In contrast, disks are random
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access media because a disk drive can access any point at random without passing through intervening points. Because tapes are so slow, they are generally used only for long – term storage and backup. Data to be used regularly is almost always kept on a disk. Tapes are also used for transporting large amounts of data. Tapes come in a variety of sizes and formats (see table 10.1). Tapes are sometimes called streamers or streaming tapes.
Type
Capacity
Description Half – inch tapes come both as 9 track reels and as
Half – inch
60 MB – 400 MB
cartridges. These tapes are relatively cheap, but require expensive tape drives. Quarter – inch cartridges (QIC tapes) are relatively inexpensive and support fast data transfer rates.
Quarter – inch
40 MB – 5 GB
QIC mini cartridges are even less expensive, but their data capacities are smaller and their transfer rates are slower. 8-mm helical – scan cartridges use the same technology as VCR tapes
8-mm Helical – scan
1GB – 5GB
and have the greatest capacity. But they require expensive tape drivers and have relatively slow data transfer rates.
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DAT (Digital Audio Tape) cartridges have the greatest 4-mm DAT
2GB-24G B
capacity but they require expensive tape drivers and have relatively slow data transfer rates.
Helical – scan Cartridge A type of magnetic tape that uses the same technology as VCR tapes. The term helical scan usually refers to 8-mm tapes, although 4-mm tapes (called DAt tapes ) uses the same technology. The 8-mm helical – scan tapes have data capacities from 2.5GB to 5GB. DAT
Cartridge DAT (Digital Audio Tape) is a type of magnetic tape that uses an ingenious
scheme called helical scan to record data. A DAT cartridge is slightly larger than a credit card and contains a magnetic tape, that can hold from 2 to 24 gigabytes of data. It can support data transfer rates of about 2 MBps (Million bytes per second). Like other types of tapes, DATs are sequential – access media. The most common format for DAT cartridge is DDS (digital data storage) which is the industry standard for digital audio tape (DAT) formats. The latest format, DDS-3, specifies tapes that can hold 24 GB (the equivalent of over 40 CD-ROMs) and support data transfer rates of 2 MBps.
WINCHESTER DISK The term Winchester comes from an early type of disk drive developed by IBM that stored 30 MB and had a 30– millisecond access time; so its inventors named it a Winchester in honor of the 30-caliber rifle of the same name. Although modern disk drives are faster and hold more data, the basic technology is the same, so Winchester has become synonymous with hard disk. HARD DISK Hard disk is a magnetic disk on which you can store computer data. The hard is used to distinguish it from a soft, or floppy, disk. Hard disks hold more data and are faster than floppy disks.
A hard disk, for example, can store anywhere from 10
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megabytes to several gigabytes, whereas most floppies have a maximum storage capacity of 1.4 megabytes. A single hard disk usually consists of several platters. Each platter requires two read/write heads, one for each side. All the read/write heads are attached to a single access arm so that they cannot move independently. Each platter has the same number of tracks, and a track location that cuts across all platters is called a cylinder. For example, a typical 84 megabyte hard disk for a PC might have two platters (four sides) and 1,053 cylinders In general, hard disks are less portable than floppies, although it is possible to buy removable hard disks. There are two types of removable hard disks : disk packs and removable cartridges.. FLOPPY DISK Floppy disk is a soft magnetic disk. It is called floppy because it flops if you wave it (at least, the 5
1/4
– inch variety does). Unlike most hard disks, floppy disks (often
called floppies or diskettes) are portable, because you can remove them from a disk drive. Disk drives for floppy disks are called floppy drives. Floppy disks are slower to access than hard disks and have less storage capacity, but they are less expensive and are portable. Floppies come in two basic sizes: •
5
1/4
– inch – The common size for PCs made before 1987. This type of
floppy is generally capable of storing between 100K and 1.2 MB (megabytes) of data. The most common sizes are 360 K and 1.2MB. •
3
1/2_
inch – Floppy is something of a misnomer for these disks, as they
are encased in a rigid envelope. Despite their small size, microfloppies have a larger storage capacity than their cousins – from 40K to 1.4MB of data. The most common sizes for PCs are 720K (double - density) and 1.44MB (high- density). Macintoshes support disks of 400K, 800K, and 1.2MB. ZIP DISK These are high – capacity floppy disk drives developed by the Iomega Corporation. Zip disks are slightly larger than the conventional floppy disks, and are about twice as thick.
They can hold 100MB of data.
Because they’re relatively
inexpensive and durable, they have become a popular media for backing up hard disks and for transporting large files.
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JAZ DISK These are removable disk drivers developed by the Iomega Corporation. The Jaz drive has a 12-ms average seek time and a transfer rate 5.5 Mbps .The removable cartridges hold 1GB of data. The fast rates and large storage capacity make it a viable alternative for backup storage as well as everyday use.
SUPER DISK This is a new disk storage technology developed by the Imation Corporation that supports very high-density diskettes.
SuperDisk diskettes are etched with a servo
pattern at the factory. This pattern is then read by the SuperDisk drive to precisely slign the read/write head. The result is that a SuperDisk diskette can have 2,490 tacks, as opposed to the 135 tacks that conventional 3.5 – inch 1.44 MB diskettes use. This density translates into 120MB capacity per diskette. OPTICAL DISK Optical Disks are a storage medium from which data is read and to which it is written by lasers. Optical disks can store much more data – up to 6 gigabytes (6 billion bytes)- than magnetic media, such as floppies and hard disks. There are three basic of optical disks: •
CD-ROM - Like audio CDs, CD-ROMs come with data already encoded onto them. The data is permanent and can be read any number of times, but CDROMs cannot be modified.
•
WORM – This term stands for write – once, read many. With a WORM disk drive, you can write data onto a WORM disk, but only once. After that, the WORM disk behaves just like a CD-ROM.
•
Erasable - Optical disks that can be erased and loaded with new data, just like magnetic disks. These are often referred to as EO (erasable optical) disks.
CD – ROM CD – ROM, which is pronounced as ‘see – dee - rom’, is the abbreviation of Compact Disc – Read – Only Memory. CD – ROM is a type of optical disk capable of storing large amounts of data - up to 1GB, although the most common size is 630 MB (megabytes). A single CD – Rom has the storage capacity of 700 floppy disks, enough memory to store about 300,000 text pages. CD – ROMs are recorded by the vendor, and once recorded, they cannot be erased and filled with new data. To read a CD, you need a CD – ROM player. Also
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called a CD – ROM drive, a CD – ROM player is a device that can read information from a CD – ROM. There are a number of features that distinguish CD – ROM players, the most important of which is probably their speed. CD– Rom players are generally classified as single – speed or some multiple of single – speed. For example, a 4X player access data at four times the speed of a single – speed player. Within these groups, however, there is some variation. Also, you need to be aware of whether the CD – ROM uses the CLV (Constant Linear Velocity) or CAV (Constant Angular Velocity) technology. Two more precise measurements are the drives seek time and data transfer rate. The seek time, also called the access time, measures how long, on average; it takes the drive to access a particular piece of information. The data transfer rate measures how much data can be read and sent to the computer in a second. Most CD –ROMs connect via a SCSI bus. Other CD – ROMs connect to an IDE or enhanced IDE interface, which is the one used by the hard disk drive. CD – ROMs are particularly well suited to information that requires large storage capacity.
This
includes color graphics, sound, and especially video. CD – R Drive CD – R drive which is short for Compact Disk – Recordable drive, is a type of disk drive that can create CD- ROMs and audio CDs. This allows the users to “master” a CD – Rom or audio CD for publishing. Until recently, CD – R drives were quite expensive, but prices have dropped dramatically. A feature of many CD – R drives, called multisession recording, enables you to keep adding data to a CD – ROM over time. This is extremely important if you want to use the CD – R drive to create backup CD – ROMs. To create CD – ROMs and audio CDs, you’ll need not only a CD – R drive, but also a CD – R software package .Often, it is the software package, not the drive itself that determines how easy or difficult it is to create CD – ROMs. CD – R drives can also read CD – ROMs and play audio CDs. CD – RW Disks CD – RW disk is short for CD Rewritable disk and this is a new type of CD disk that enables you to write onto it in multiple sessions. One of the problems with CD – R disks is that you can only write to them once. With CD – RW drives and disks, you can treat the optical disk just like a floppy or hard disk, writing data onto it multiple times.
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The first CD – RW drives became available in mid – 1997. They can read CD– ROMs and can write onto today’s CD – R disks, but they cannot write on CD – ROMs. Many experts believe that they’ll be a popular storage medium.
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UNIT – II COMPUTER SOFTWARE INTRODUCTION A computer needs both hardware and software for its proper functioning. By software we mean computer instructions or data. Anything that can be stored electronically in software. The storage devices and display devices are hardware. Software and hardware are used as both nouns and adjectives. For example, you can say – “The problem lies in the software,” which means that there is a problem with the program or data, not with the computer itself. You can also say: “It’s a software problem.” The distinction between software and hardware is sometimes confusing because they are so integrally linked. Clearly, when you purchase a program, you are buying software. But to buy the software, you need to buy the floppy or CD-ROM (hardware) on which the software is recorded. Note: other than software and hardware there is something called firmware. Firmware are software (programs or data) that has been permanently written onto read-only memory (ROM). Firmware is a combination of software and hardware. ROM s and PROM s that have data or programs recorded on them are firmware.
Software is often divided into two categories. System software - Includes the operating system and all the utilities that enable the computer to function. Applications software - Includes programs that do real work for users. For example, word processors, spreadsheets, and database management system fall under the category of application software. As mentioned above software can be divided into two general classes. System software and application software. System software consists of low-level programs that interact with the computer at a very basic level. This includes operating systems, compilers, and utilities for managing computer resources. In contrast, applications software (also called
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end-user programs) includes database programs, word processors, and spreadsheets. Figuratively speaking, applications software sits on top of system software because it is unable to run without the operating system and system utilities.
The figure 12.1 gives an overview of the software classification and the different
SOFTWARE
software types.
Systems software
Applications software
Word processors
Image Processors
Operating systems
FileMgmt.Tools
Spreadsheets
Data bases
Assemblers
Compilers
Communication Software
Games
Debuggers
Utilities
Figure 12.1 Software Types Now we will have an overview of these different classes of software – primarily operating systems, compilers, utilities, word processors, spread sheets database management systems, etc.
OPERATING SYSTEMS Operating systems are the most important programs that run on a computer. Every general purpose computer must have an operating system to run other programs. Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and dictionaries on the disk, and controlling peripheral devices such as disk drives and printers. Most commonly used operating systems include Microsoft Windows, DOS, Xenix, Mac OS, OS/2, UNIX, MVS, etc.
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UTILITIES Utility is a program that performs a very specific task, usually related to managing system resources. Operating systems contain a number of utilities for managing disk drives, printers and other devices.
Utilities differ from applications mostly in terms of size and complexity. For example, word processors, spreadsheet programs, and database applications are considered applications because they are large programs that perform a variety of functions not directly related to managing computer resources.
COMPILERS & INTERPRETERS Compiler is a program that translates source code into object code. The compiler derives its name from the way it works, looking at the entire piece of source code and collecting and reorganizing the instructions. Thus, a compiler differs from an interpreter, analyzes and executes each line of source code in succession, without looking at the entire program. The advantage of interpreters is that they can execute a program immediately. Compilers require some time before an executable program emerges. However, programs produced by compilers run much faster than the same program executed by an interpreter. PROGRAMMING LANGUAGES INTRODUCTION If you want to get something done by a person, you will tell him what to do in a language that he understands. Similarly, if you want to make the computer to do some task for you, you have to tell the computer what to do in a language that the computer understands – machine language, which in the printed form is apt to be an incomprehensible page after page of ones and zeros. How can you then communicate with the computer?
To communicate with the computer is to develop a third language – a language that can be understood by both you and computer. This is what a programming language is –
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a set of rules that provides a way of instructing the computer to perform certain operations.
Programming languages are said to be lower or higher, depending on whether they are closer to the language the computer itself uses (lower, which means 0s and 1s , as we shall explain) or to the language that people use (higher means more English like). In this chapter we shall consider the five levels (or generations) of language.
1. Machine Languages / First generation Languages. 2. Assembly Languages / Second generation Languages. 3. Procedural Languages / Third generation Languages. 4. Problem-oriented Languages / Fourth generation Languages. 5. Natural Languages / Fifth- generation Languages.
The high-level languages – such as Pascal, BASIC, and COBOL – are the ones used to code application programs, so we shall emphasize them. The closer the level is to human speech, the more it is described as a “user-friendly” language. The term userfriendly, incidentally, is one that is used a great deal throughout the computer industry.
MACHINE LANGUAGES We think of computers as being quite complicated, but actually their basis is very simple. They rest on the concept of electricity being turned “on” and “off”. From this on/off, yes/no, two state system, sophisticated ways of representing data have been constructed using the binary system of numbers. The binary system is based on two digits – 0 and 1.
By contrast, the decimal system that we all use is based on ten digits – 0 through 9. The numbers 1, 2 and 3 in the decimal system are represented in the binary system as 1, 10 and 11 respectively. Letters of the alphabet are also represented as numbers. In one system, the letter A is represented as 1000001. Commas, semicolons and other special characters are also represented as bunches of 0s and 1s.
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In the early days of computers, with machines as the ENIAC, which uses vaccum tubes, one could actually see the tubes lit up or unlit, corresponding to the 1/0 binary state – the switch was either on or off.
For example, consider a line from a program segment, which multiplies two numbers. 11110010 01110011 11010010 00010000 01110000 00101011 Clearly, working with this kind of code is not for everybody.
ASSEMBLY LANGUAGES From the above discussions it became that working with 0s and 1s could turn people themselves into ciphers. In the 1950s, to reduce programming complexity and provide some standardization, assembly languages were developed. Assembly languages, also known as symbolic languages use abbreviations or mnemonic codecodes more easily memorized –to replace the 0s and 1s of machine languages.
The machine language segment we saw above is as follows: 11110010
01110011 11010010 00010000 01110000 00101011
This could be expressed in assembly language statement as: PACK 210 (8, 13), 02B (4, 7)
Actually, assembly languages do not replace machine languages. In fact, for an assembly language program to be executed, it must be converted to machine code. The assembly language program is referred to as a source program where as, the machine language program is an object program.
HIGH LEVEL LANGUAGES High Level Languages assisted programmers by reducing further the number of computer operation details they had to specify, so that they could concentrate more on the logic needed to solve the problem.
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To see this, you need only to look at the code segments, in which the same instruction – “Calculate gross pay”- is expressed in three different languages: machine, assembly and COBOL.
Machine Language: 11110010 11110010 11111100 11110000 11110011 10010110
01110011 01110011 01010010 01000101 01000011 11110000
1101 1101 1101 1101 0111 0111
001000010000 001000011000 001000010010 001000010011 000001010000 000001010100
0111 0111 1101 0000 1101
000000101011 000000101111 001000011101 000000111110 001000010100
Assembly Language:
PACK 210 (8, 13), 02B (4, 7) PACK 218 (8, 13), 02F (4, 7) MP
212 (G, 13), 21D (4, 7)
SRP
213 (5, 13), 03E (0), 5
UNPK 050 (5, 7), 214 (4, 13) IO
054 (7), X ‘FO’
COBOL: MULTIPLY HOURS-WORKED BY PAY-RATE GIVING GROSS-PAY ROUNDED.
TYPES OF HIGH LEVEL LANGUAGES Languages are often referred to as generations, the idea being that machine languages were the first generation and assembly languages were the second generation. High-level languages are sometimes used to refer all languages above the assembly level. Here we will subdivide high –level languages into three generations. •
Procedural-oriented or third generation
•
Problem-oriented or fourth generation
•
Natural or fifth generation.
Procedural-oriented Languages
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High-level languages are often classified according to whether they solve general problems or specific problems. General-purpose programming languages are called procedural languages or third generation languages. They are languages such as Pascal, BASIC, COBOL, and FORTRAN, which are designed to express the logic, the procedure, of a problem. Because of their flexibility, procedural languages are able to solve a variety of problems.
Problem-oriented Languages and Application Generators Third generation languages, such as BASIC or Pascal, require you to instruct the computer in step-by-step fashion. Fourth-generation languages, also known as problemoriented languages, are high-level languages designed to solve specific problems or develop specific applications by enabling you to describe what you want rather than step-by-step procedures for getting there. Personal Computer applications software: You have already been introduced to application software for PCs, but the ones we are particularly concerned with here are word processors, spreadsheets, database managers, business graphics and integrated packages. Query languages and report generators : Query languages allow people who are not programmers to search a database using certain selection commands. Query languages, for example, are used by airline or railway reservations personnel needing ticket information. Report generators are designed for people needing to prepare reports easily. Examples of query languages and report generators include QBE, SQL, HAL, ANSWER/DATABASE, DATATRIEVE, EASYTRIEVE PLUS, Honeywell PDQ, INQUIRE, INTELLECT, QMT, RPG III, etc.
DATA PROCESSING INTRODUCTION Data Processing also known as information processing is defined as the processing of data to make it more usable and meaningful, thus transforming it into information.
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DATA VERSUS INFORMATION The word data is the plural of datum, though data is commonly used to represent both singular and plural form. Data is commonly defined as raw facts or observation, typically about physical phenomena or business transaction. For example, a spacecraft launch or the sale of an automobile would generate a lot of data describing those events. More specifically, data are objective measurements of the attributes (the characteristics) of entities (such as people, place, things and events). These measurements are usually represented by symbols such as numbers and words, or by codes composed of a mixture of numerical, alphabetical, and other characters. However, data commonly takes a variety of forms including numeric data, text, voice and images. The term data and information are often used interchangeably. However, it is helpful to view data as raw material that are processed into finished information products. Information can then be defined as data that has been transformed into a meaningful and useful context for specific end user. However, data is usually not useful until subjected to a value added process where: 1. Its form is aggregated, manipulated and organized. 2. Its content is analyzed and evaluated. 3. It is placed in a proper context for a human user.
FILE PROCESSING Computer data is processed in two fundamental ways: file processing and database processing. With file processing, data is stored and processed in separate files. There are two types of file processing – sequential and direct access. Sequential File Processing Sequential file processing stores and accesses records in sequence. Such processing can be accomplished either by using tape storage or disk storage. To perform sequential file processing, records are sorted before they are processed. Sequential file processing is used in situations where data can be processed in batches and where a substantial position of the master file is changed with the processing of each batch. Payroll processing is a classic example of sequential processing.
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Direct-access File Processing In some cases, where it is impractical to process the data sequentially, directaccess file processing is required. Consider the problem of authorizing credit card purchases. When you make an expensive purchase with a credit card, the merchant is required to verify your credit card and limit. To do this, the merchant accesses a computer system that maintains a file of credit card numbers, status (valid, lost, stolen, etc.), and the available credit. It is impractical to store this data sequentially. Both you and the merchant would become quite impatient if you to wait 30 minutes for the computer system to sequentially process the file down to the point of your record. Clearly, direct-access to your record is required. Problems with File Processing File processing is adequate for many information systems, and, in fact, it has been the backbone of the computer industry for many years. For some applications, however, it has disadvantages.
First, observe that data is duplicated. Such duplications waste file space. There is an even more serious disadvantage. When the same data is stored in two or more places, the possibility exists that the value will come to disagree with one another. A second disadvantage of file processing is the difficulty of relating records in one file to records in another. File processing is gradually being replaced by the second type of data processing – database processing.
DATABASE PROCESSING A database is a self-describing collection of integrated records. It is a selfdescribing because it contains, as part of itself, a dictionary, or dictionary, of its contents. The records are integrated because a database can contain multiple files (usually called tables in database processing), and the records within those tables are processed by their relationship to one another.
In database processing, the database management system (DBMS) acts as an intermediary between the user, or application program, and the database. The DBMS stores and processes the data so that records can be accessed via their relationship to
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other records. When a user wants to produce a report using data reading in two tables, the user can submit a request and the DBMS, based on the relationship of the data items will combine and collate the information from the related table and will give it to the user. The maintenance of the relationships, data integrity and other related tasks are taken care of by the DBMS. OPERATING SYSTEMS INTRODUCTION An operating system manages and coordinates the function performed by the computer hardware, including the CPU, input/output devices, secondary storage devices, and communication and network equipment. Operating systems are the most important programs that run on a computer. The operating system software must keep track of each hardware resource, determine who gets what, determine when the user will have access to the resource, allocate how much of the user will be given , and terminate access at the end of the use period. Functions Of An Operating System Even the simplest operating system in a minicomputer or mainframe performs a number of resource management tasks or functions. These functions include job management, batch processing, on-line processing, data management, virtual storage, and input/output management. Job Management Job management software manages the jobs waiting to be processed. It recognizes the jobs, identifies their priorities, determines whether the appropriate main memory and secondary storage capability they require is available, and schedules and finally runs each job at the appropriate moment.
Batch Processing System software is available to support the different methods of processing a job. With batch processing the most basic method, data are accumulated and processed in groups. Payroll applications, for example, are often processed this way. Once in every week, hourly records are grouped and the payroll software is run.
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On-line Processing In on-line processing, data are processed instantaneously. For example, a sales person may need to find out whether a particular item requested by a customer is in stock for immediate shipment.
Data Management In the process of managing the resources of the computer system, operating system software also manages the storage and retrieval of data. As the system software handles many of the details associated with this process, such details are not a primary concern for users or programmers writing application programs. Virtual Storage Operating systems have a feature called virtual storage. This is accomplished by breaking a job into sequences of instructions, called pages or segments, and keeping only a few of these in main memory at a time, the remainder are kept on secondary storage devices. As a result, relatively large jobs can be processed by a CPU that in fact contains a relatively small memory. Input/Output Management Operating systems also manage the input to and output from a computer system. This applies to the flow of data among computers, terminals, and other devices such as printers. Application programs use the operating system extensively to handle input and output devices as needed.
CLASSIFICATION OF OPERATING SYSTEMS
Operating systems can be classified as follows:
Multi-user
Multi-user operating systems allow two users to run programs at the same time. Some operating systems permit hundreds or even thousands of concurrent users. The
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operating systems of mainframes and minicomputer are multi-user systems. Examples are MVS, UNIX, etc. Another term for multi-user is time-sharing. Multiprocessing Multiprocessing refers to a computer system’s ability to support more than one process (program) at the same time. Multiprocessing operating systems enable several programs to run concurrently.MVS and UNIX is two of the most widely used multiprocessing systems, but there are many others, including OS/2 for high-end PCs.
Multitasking
Multitasking allows more than one program to run concurrently. Multitasking is the ability to execute more than one task at the same time, a task being a program. The terms multitasking and multiprocessing are often used interchangeably, although multiprocessing sometimes implies that more than one CPU is involved. Multithreading
Multithreading allows different parts of a single program to run concurrently. Multithreading is the ability of an operating system to execute different parts of a program, called threads, simultaneously. The programmer must carefully design the program in such a way that all the threads can run at the same time without interfering with each other.
Real-time
Real-time operating systems are systems that respond to input immediately. This category includes operating systems designed substantially for the purpose of controlling and monitoring external activities with timing constraints. COMPUTER NETWORKS INTRODUCTION End-users need to communicate electronically in today’s world. People need to exchange data and information electronically with one another. A good communication
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system is a must of every organization. Organization depends on interconnected networks of computers to service their information processing needs. A network is a group of two or more computer systems linked together.
OVERVIEW OF A NETWORK Generally a communications network is any arrangement where a sender transmits a message to a receiver over a channel consisting of some type of medium.
Terminals
Terminals include video display terminals and other end-user workstations. Any input /output device that use a network to transmit or receive data is a terminal. This includes microcomputers, telephones, fax machine, etc.
Telecommunication Processor These are devices, which support data transmission and reception between terminals and computers. These devices such as modems, multiplexers and front-end processors, perform a variety of control and support functions in a network.
Telecommunications Channels and Media
The media over which data are transmitted and received called telecommunication channels. Telecommunication channels use combinations of media, such as copper wires, coaxial cables, fiber optic cables, microwave systems and communication satellite systems to interconnect the other components of a network. Computer
Networks interconnect computer of all sizes and types so that they can carry out their information processing assignments. Telecommunication Software
Telecommunication software consists of programs that reside in host computer systems, communication control computers and end user computers. This controls the
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telecommunication activities of the computer systems and manages the functions of networks. COMMUNICATION PROCEESORS
Communication processors resemble computer CPUs in that they have similar circuitry, have memories, and can be programmed, but their purpose is limited – to enhance data communications between two points. Communication processors include the following: modems, message switchers, multiplexers, concentrators and controllers, and front-end processors. Modems
Modems are the most communication processors. They convert the digital signal from a computer or terminal at one end of a communications link into analog signals, which can be transmitted over ordinary telephone lines. A modem at the other end of the communications line converts the transmitted data back into digital form at the receiving terminal. The process is known as modulation and demodulation, and the word modem is a combined abbreviation of those two words. Modems come in several forms including small stand- alone units, plug- in circuit boards and micro electronic modem chips. Message Switchers Message switchers are a processor that receives data messages from terminals, determines their destination, and routes them one at a time to the CPU. It distributes the messages coming from the CPU to the appropriate terminal. Multiplexers, Concentrators, and Controllers Like message switchers, a multiplexer allows several terminals to use one line to communicate with a CPU. However, it allows the terminals to send their messages simultaneously. A multiplexer, in other words, collects messages from various senders, put them in order, and transmits them along a broadband channel at very high speeds to the receiver.
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A concentrator is essentially a smart multiplexer – it can be programmed, has more processing capability, and is more flexible than a multiplexer.
Controllers or cluster controllers, link groups of terminals or other devices to a communications channel. The controller polls the status of each terminal and transfers data from a terminal to the host computer when necessary. Front-end Processors A front-end processor is located at the site of the CPU or the host computer and its purpose is to relieve the central computer of some of the communications tasks, leaving the larger computer free for processing application programs. Here we can see that communication processing and data processing equipment are nearly alike. Indeed, front-end processors are computers – they have some identical circuitry and perform many of the operations that a data processing equipment perform.
COMMUNICATIONS MEDIA Channels also called communication lines or links are the means by which data is transmitted between the sending and receiving devices in a network. A channel makes use of a variety of media. These include twisted-pair wire, coaxial cables and fiber optic cables, all of which physically link the devices in a network. Twisted- pair Wire This is the oldest and still most common transmission line and consists of copper wires twisted into pairs. These lines are used in established communications networks throughout the world for both voice and data transmission. Coaxial Cable Coaxial cable consists of a sturdy copper or aluminum wire wrapped with spacers to insulate and protect it. The insulation minimizes the interference and distortion of the signals the cable carries. Groups of coaxial cables may be bundled together in a big cable for ease of installation. These high quality lines can be placed underground and laid on the floors of lakes and oceans. They allow high-speed data transmission.
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Fiber Optic Cables Fiber optics use cables consisting of one or more hair-thin filaments of glass fiber wrapped in a protective jacket. They can conduct light pulses generated by lasers at transmission rates as high as 2 billion bits per second. This is about ten times greater than coaxial cables and 200 times better than twisted-pair wires. Fiber optic cables provide substantial size and weight reduction as well as increased speed and greater carrying capacity.
Microwave System Terrestrial (earth bound) microwave systems transmit high -speed radio signal in a line -of- site path between relay station spaced approximately 25 to 35 miles apart. Because the waves cannot bend with the curvature of the earth, they are relayed via antennas usually placed on top of buildings, towers, hills and mountain peaks.
Communications Satellites Communications satellites in space orbiting 22,000 miles above the earth are also used as microwave relay stations because they rotate at the precise point and speed above the equator that makes them appear stationary to microwave transmitters on the ground. Among the dozens of satellites now orbiting the earth and handling voice, video and data communications are those launched by INTELSAT, short for International Telecommunications Satellite Consortium.
TYPES OF NETWORKS
There are many different types of networks. However from an end user’s point of view there are two basic types. •
Local- area networks (LANs) – The computers are geographically close together (that is, in the same building).
•
Wide-area networks (WANs) - The computers are farther apart and are connected by telephone lines or radio waves.
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In addition to these types, the following characteristics are also used to categorize different types of networks. •
Topology - The geometric arrangement of a computer system. Common topologies include a bus, star, and ring.
•
Protocol – The protocol defines a common set of rules and signals that computers on the network use to communicate. One of the most popular protocols for LANs is called Ethernet. Another popular LAN protocol for PCs is the IBM token- ring network.
•
Architecture – Networks can be broadly classified as using either peer-topeer or client / server architecture.
NETWORK TOPOLOGIES As we have seen earlier, topology is the geometric arrangement of the computers in a network. Common topologies include star, ring and bus.
Star Network
The star network is frequently used to connect one or more small computers or peripheral devices to a large host computer or CPU. Many organizations use the star network or a variation of it in a time- sharing system, in which several users are able to share a central processor. Ring Network
The ring network is a local- area network (LAN) whose topology is a ring – can be as simple as a circle or point-to-point connections of computers at dispersed locations, with no central host computers or communications controller. That is, all of the nodes are connected in a closed loop. Messages travel around the ring, with each node reading those messages addressed to it. One of the advantages of ring networks is that they can span larger distances than other types of networks, such as bus networks, because each node regenerates messages as they pass through it.
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Bus Network Bus networks are similar to ring networks except that the ends are not connected. All communications are carried on a common cable or bus and are available to each device on the network. Access and control of bus networks are typically maintained by a method called contention, whereby if a line is unused, a terminal or device can transmit its message at will, but if two or more terminals initiate messages simultaneously, they must stop and transmit again at different intervals.
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UNIT-III COMMUNITIONS SYSTEMS INTRODUCTION Communication is the transmission of data from one computer to another, one place to another or from one device to another. A communications device, therefore, is any machine that assists data transmission. For example, Radio, TV, Satellite, etc. are all communications devices.
RADIO A radio receiver in its simplest form comprise of an input circuit for tuning into the frequencies of the various transmitters to be received, a demodulation circuit for separating audio frequencies from the high-frequency carrier waves, a low-frequency Television Camera and Scanning The television camera is the first tool used to produce a television program. Most cameras have three basic elements: an optical system (lenses) for capturing a image, a pickup device for translating the image into electronic signals, and an encoder for encoding the signals so that they may be transmitted. In color television, signals from three tubes within the camera are sent to the encoder, which combines them into a single electronic signal. Television cameras and television receivers use a procedure called scanning to record visual images and re-create them on a television screen. The television camera breaks an image into a series of lines and scans over each lie with a beam of electrons. The camera must scan a scene many times per second to record a continuous image. In the television receiver, another electron beam uses a similar scanning process to reproduce the original image on the receiver’s screen.
Transmission of Television Signals The high-frequency waves radiated by transmitting antennas can travel only in a straight line, and may be blocked by obstacles. For this reason, transmitting antennas must be placed on tall buildings or towers. Cable television was first developed in the lat 1940s to serve areas that were blocked from receiving signals. The signal is picked up on a receiver and redistributed by cable. Viewers in most areas can now subscribe to
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cable television services that provide a wide variety of television programs and films transmitted by cable to the viewer’s television set. Network television stations use microwave relay stations to broadcast to affiliates far from the original source of the broadcast. Communications satellites also receive television signals from a ground station and relay them back to specified areas. Satellite transmissions are used to efficiently distribute television and radio programs from one geographic location to another. In addition, direct-broadcast satellite deliver television programming directly to individual receivers through small home dishes.
MICROWAVE SYSTEMS Microwave transmission consists of high-frequency waves (1000 – 3000MHz) that travel in straight lines through the air rather than through wires. A microwave system consists of towers located at intervals of 25 to 30 miles on which dish-like antennas are mounted. Because the waves cannot bend with the curvature of the earth, these towers must be within the line-of-sight from one another. When one tower receives the signal, in amplifies the signal and sends it to the next tower.
Communications satellites in space, orbiting in the Clarke orbit are also used as microwave relay stations because they rotate at the precise point and speed above the equator that makes them appear stationary to the microwave transmitted on the ground.
Microwaves systems have the capacity to carry large quantities of data – both digital and analog at high rates of speed. They are used for the transmission of television and telephonic signals.
COMMUNICATIONS SATELLITES Satellites have now become a integral part of the worldwide communications systems. Although long-range and long-distance communications took place much before the introduction of satellite systems, they had a lot of disadvantages. Point-topoint communication systems are very difficult in the case of remote and isolated locations – locations, which are surrounded by oceans, mountains and other obstacles created by nature. The satellite is nothing more than a radio-relay station. But they
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have one potential advantage – the capability of a direct line –of-sight path to 98% (excluding the polar caps, which are inaccessible to satellites) of the earth’s surface. One of the most important event in the history of satellite communications took place when COMSAT or Communications Satellite Corporation, launched four satellites within 6 years that is between 1965 to 1979. The first of these series was the ‘Early Bird’, which was launched in 1965. This was the first communications station to handle worldwide commercial telephone traffic from a fixed position in space. The next series, INTELSAT was a group of satellites that several 150 stations in 80 countries.
The Satellite Orbit The communications satellites are placed in orbits called equatorial geosynchronous orbit. The satellite place in this orbit will appear stationary over a selected location on the earth’s surface. So, communications satellites are placed in an orbit that is directly over the equator, moving in a west-to east direction at an altitude of 22,282 miles above sea level and with a forward velocity of 6874 mph to complete one orbit in 24 hours. This orbit is called the Clarke orbit. Up-link and Drawn-link All of the ground equipment along with the transmission path and receiving antenna at the satellite are included in the up-link system. Basically this includes everything before the input terminals of the satellite receiver. The down-link is described in terms of satellite transmitter output power, down-link antenna gain beam-width and the ground area that the transmitted signal will cover – the footprint.
Cross-link At the altitude of the Clarke orbit, one satellite could command a footprint area of 42.2% of the earth’s surface. The beam-width from the satellite for such coverage is 17.2 degrees. Since such a satellite is not sufficient for global coverage, we need more than one (to be specific, 3) satellite. These three satellites are placed, 120 degrees apart in the Clarke orbit and would cover the earth’s entire surface except for the polar caps. This makes is possible for one earth station to transmit to another station on the opposite side of the globe by sending data to its ‘in-view’satellite, from which it is transmitted to its closest neighbour in the Clarke’s orbit and from there back to the earth.
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The cross-link distance is 45,458 miles between the satellites, making the total ‘earth-satellite-satellite-earth’ distance 90,014 miles. A message would take about 0.5 seconds to travel this distance or almost one second if a return response is needed. ITELSAT was the first to set up such a communication link, with satellites spaced over the Indian, Atlantic and Pacific Oceans above the equator.
Components of a Satellite There are five major components in a satellite. They are: •
The Transponder
•
The Antenna System
•
The Control and Information System
•
The Rocket Thruster System
•
The transponder is a high –frequency radio receiver, a frequency downconverter and a power amplifier, which is used to transmit the down-link signal. The antenna system contains the The Power Package antennas and the mechanisms to position tem correctly. Once properly in place, they will generally function trouble-free for the life of the satellite. The power package is the power supply to the satellite. The satellite must b powered either from a battery or solar system. In the case of
communications satellites in the Clarke orbit, a combination of battery power and solar energy is used. A solar cell system supplies the power to run the electronics ad charge the batteries the sunlight cycle and the battery furnishes the energy during the eclipse. The control and information system and the rocket thruster system are called the Station Keeping system. The function of the station keeping system is to keep the satellite in the correct orbit with the antennas pointed in the exact direction desired. RADAR The name ‘radar’ is the acronym of Radio Detecting and Ranging. It denotes the method of scanning the surrounding space by means of high frequency radio waves, which are sent out from a powerful transmitter and are reflected by any objects, which they encounter. The reflected beam is picked up by a receiver and its strength and direction gives information on the size, distance, altitude, etc. of the object. If for example, an observer in an aircraft wishes to survey by radar the terrain over which he is flying, a rotating radar beam is directed downward from the aircraft.
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The beam scans a circular area in the form of a sector, which sweeps round and round. Depending on the nature of the reflecting objects the intensity of the reflected beam will vary . The transmission and reception of the high frequency waves are effected in the radar apparatus. Figure 19.7 shows a ground radar installation. The Radar waves are generated in the transmitted, which is equipped with radio tubes of special design. The transmitting antenna usually also functions as the receiving antenna. This process is called periodic changeover. The receiver picks up the reflected beam and the corresponding electronic circuits are used to deflect an electron beam in a cathode ray tube (CRT). The beam is so deflected that it scans the luminescent screen from the center to the edge while it rotates at the same speed antenna. An echo picked up by the receiver strengthens the flow of electrons in the CRT, causing a point of light to appear on the screen and to remain visible by phosphorescent afterglow until fresh echoes are picked up on the next revolution of the scanning antenna. In this way the points of light build up a picture of the area scanned by the radar beam. The brightness of the display of the signal (the radar echo) on the luminescent screen of the CRT depends on the reflecting power of the object with regard to the high- frequency radio waves sent out by the radar transmitter. For this reason, a radar image generally looks quite different from an optical image, though as a rule they have the same outlines. Most radar sets employ pulse radar. This is so called because the transmitter sends out short intense bursts or pulses of energy with a relativity long interval between the pulses. The receiver is active during this interval. When sufficient time has elapsed to permit the reception of echoed from the most distant objects of interest, the transmitter sends another short pulse and the cycle is repeated.
FIBER OPTICS Fiber optics can be described as a transmission system employing a lightemitting source – turned on and off rapidly by, electrical, impulses – whose emissions are sent through a glass pipe to a light-sensitive receiver to convert the changing light intensities back into electrical impulses. The ‘core’ of a fiber optic cable is a very thin strand of highly refined cylindrical glass. The glass core of the cable may have a diameter as small as 4.5 um (2/10,000
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inch) or as large as 400um. A second layer of glass called the clad surrounds the core. The clad is fused directly to the core so that it is very difficult to see the boundary between the two with naked eyes. The clad has a different optical density from the core material. Fiber optics is founded on the theory of reflection that results at the interface between two materials of different densities. They can conduct light pulses generated by lasers at transmission rates as high as 2 billion bits per second.
Advantages and Disadvantages Some of the advantages of fiber optic systems are: •
The main ingredient in glass is sand and there is an enormous supply of sand in the world compared to the supply of Copper and Aluminum.
•
Photons of lights, rather than the an electrical current move through the optic fiber. Therefore, there is no chance of a spark flash thereby making this system safer.
•
Since
the fiber system carries no electrical current, the energy
transmitted through the fiber cannot radiate radio frequency interference, nor can it be contaminated by any external noise or radio frequency fields. •
It is nearly impossible to eavesdrop on fiber optic systems without being easily detected. Because of the absence of current flow through the fiber, intrusion into the system is also prevented. Confidential information cannot be routed to unwanted receivers, nor can false information be fed into the data steam.
•
The transmission losses of fiber optic cables are much lower than that of the twisted-pair wires and coaxial cables.
•
Fiber optic cables provide substantial size and weight reduction as well as increased speed an greater carrying capacity. A half-inch diameter fiber optic cable can carry up to 50,000 cannels, compared to about 5,500 channels standard coaxial cable.
•
Glass is immune to corrosive and oxide degradation and will stand up well in hostile environments.
•
The size of the core and clad of a single fiber conductor is much smaller than the diameter of the common copper wire and since fiber optic cables
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are not affected by and do not generate electromagnetic radiation; therefore, multiple fibers can be placed in the same cable. Some disadvantages of the systems are: •
All fiber optic systems are limited to fixed point-to-point ground installations. They cannot leave the ground or be associated with a mobile communication station.
•
Popular light-emitting source can be modulated are limited.
•
The ways in which the light source can be modulated are limited.
•
Because of low-power sources, the distance between repeater amplifiers must be relatively short for high data rates demanded in some systems.
ISDN ISDN is a high-speed, fully digital telephone service. Just as compact discs have made recorded music digits; ISDN upgrades today’s analog telephone network to a digital system. ISDN can operate at speeds up to 128 kilobits/second, which is five or more times faster than today’s analog modems. ISDN can dramatically speed up transfer of information over the Internet or over a remote LAN connection, especially rich media like graphics, audio or video or applications that normally run at LAN speeds. ISDN stands for Integrated Services Digital Network – the name for digital telephone service that works over existing copper telephone wiring. There are several types of ISDN service, but the most appropriate type for individual computer users, and the type that this site focuses on is the ISDN Basic Rate Interface (BRI). Basic rate ISDN divides the telephone line into 3 digital channels:2 “B” channels and one “D” channel, each of which can be used simultaneously. The B channels are used to transmit data, at the rate of 64k or 56k (depending on your telephone company). The D channel does the administrative work, such as setting up and tearing down the call and communicating with the telephone network. With two B channels, you can make two calls simultaneously. Most of the world’s existing telephone networks are already digital. The only part that typically isn’t digital is the section that runs from the local exchange to your house or office. ISDN makes that final leg of the network digital. The original version of ISDN employs baseband transmission. Another version, called B-ISDN, uses broadband transmission and is able to support transmission rates of 1.5Mbps. B-ISDN requires fiber optic cables and is not widely available.
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Why is ISDN so Important? More than just a means for fast, accurate, data transmission, ISDN truly represents the next generation of the world’s telephone service for all forms of telecommunications, including voice. ISDN brings the digital network to the individual user. Thus, the same twistedpair copper telephone line that could traditionally carry only one voice, or one computer or one fax “conversation” can now carry as many as three separate “conversations” at the same time, through the same line. ISDN is the “magic” that makes this happen. How is this possible? The basic ISDN-to-user connection, called a Basic Rate interface (BRI) contains three separate channels, or “pipes.” Two of these channels (the B channels) carry user “conversations” from a telephone, a computer, a fax or almost any other device. The third channel (the D channel) carries call setup information for the network, but can also carry user data transmissions. This means that two separate “conversations”, say a voice call and a computer transmission can take place at the same time through the same ISDN line. Simultaneously, a third “conversation”, an e-mail message or a credit-card authorization, for example, could also take place through the same connection. The power of ISDN enables all three of these transmissions to happen at the same time, through the same copper twisted-pair telephone lines that once could handle only one transmission at a time. ISDN Fundamentals Integrated Services Digital Network is a set of digital transmission protocols defined by CCITT (the Consultative Committee for International Telephone and Telegraphy). These protocols are accepted virtually by all the world’s communications carriers as the standard. Some of the characteristics that distinguish ISDN are •
It builds on groups of standard transmission channels. Bearer channels (or B channels) transmit user information at relatively high speeds, while separate Delta channels (or D channels) carry call setup, signaling and other information. B channels are clear channel “pipes” for user voice and data. D channels are packet-switched links for call set-up and user data.
•
It handles all types of information. Unlike some other digital communications technologies, ISDN handles all types of information: voice, data, studio-quality
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sound, still and moving images. They are all digitized, and transmitted at high speeds in the same flow of data. •
It handles many devices and many telephone numbers on the same line. Up to eight separate telephones, fax machines or computers can be linked to a single ISDN connection, and have up to 64 “call appearances” of the same of different telephone numbers.
•
It supports up to three calls at the same time. Two voice, fax or PC “conversations”, and one data “conversation” can take place at the same time , through the same ISDN connection. “always O/Dynamic ISDN” will enable the three channels to work powerfully and efficiently together, providing the best matched channel to the application at hand, improving efficiency and lowering costs.
•
It offers variable, responsive transmission speeds. Two or more channels can be combined into a single larger transmission “pipe”. Channels can be assembled as needed for a specific application (a large videoconference, for example), and then broken down and reassembled into different groups for other applications (normal voice or data transmissions). Combining B channels in this manner is called inverse multiplexing or bonding.
•
It uses switched digital connections. Perhaps, the most important single feature of ISDN, however, is that it offers inexpensive dialed digital access to worldwide telecommunications network. It is no longer necessary to lease costly dedicated lines for high-speed digital transmission, or to limit data speed and accuracy by using modems to convert digital signals to analog pulses.
Alternatives to ISDN There really aren’t a lot of alternatives today if you want more bandwidth at home or at a small business. There are a variety of faster network choices available to larger organizations, but these solutions tend to be priced beyond the reach of most individuals. For Internet access or remote access to a corporate LAN, ISDN is the only higher speed option available for most people. If you are looking for a continuous connection, such as connecting a Web server to the Internet, a dedicated frame relay or T-I line may make more sense. ISDN is a circuit-switched service, which means it is only connected when it is being used.
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Leaving ISDN connected around the clock can end up being more expensive than a dedicated line or “leased” lie, which has a flat monthly price. Over the next several years, the bandwidth bottleneck residential and small business users face will be alleviated with new technologies such as Asymmetric Digital Subscriber Line (ADSL) which works over regular telephone wires and cable modems which work over coaxial television wiring. Both of these services will offer multiple megabits per second, but it will take time to deploy these technologies.
Distributed Systems INTRODUCTION Till recently most companies and organizations used centralized for their data processing needs. But as technology improved and data processing became more complex, the load on the centralized systems increased and a new way of data processing evolved – Distributed Data Processing (DDP) or distributed processing for short. In a centralized data processing system, the CPU, the storage devices, software and the professional data processing staff are located in one central facility. All the devices in the centralized system-including multiplexers terminals and printers – converge on one central computer, even though the users may work at distant terminals. All processing and storage take place at the central location. But in distributed data processing systems, the computers, storage devices, and even some computer professionals are distributed to separate locations throughout the organization. Processing and storage may occur at several locations in the computer system – called a network. Several computers, each located at a different point or made possible the integration of these computers located at different places. Most organizations can benefit from using distributed processing. Such a system can be more responsive to its user’s needs, and it may cost less to develop and maintain than a centralized system does. DISTRIBUTING THE PROCESSING AND STORAGE FUNCTIONS Although sharing the processing function distributes the computing load to computers away from the central computer, in most cases distributed data processing is chosen because storage too can be distributed. Furthermore, the data stored at different locations can be shared among the users. The following example
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shows how these characteristics of a distributed system can help an organization use its data resources more effectively. It shows how distributed processing systems used in multi-branch banking are effective and efficient than a centralized system. In the distributed multi-branch system, minicomputers are used at the branch banks and are responsible for the local processing of services such as savings and current accounts and loans. Each machine uses a copy of the same software for these functions. A mainframe at the central facility performs all of the consolidated accounting functions and is responsible for processing both transactions through the bank’s network of automatic teller machines (ATMs) and credit card transactions. Now, let us consider how the ATM application works. When a customer initiates a withdrawal transaction, the data associated with request are first sent to the central computer. Than the branch at which the customer’s records are maintained must be determined and the request forwarded to the appropriate branch computer. The branch computer performs a search to verify the costumer’s account and determines whether the balance in the account is adequate. If there is enough money in the account, the depositor’s record will be updated to reflect the withdrawal. Next, the data are returned to the ATM, and the machine dispenses the cash and prints a receipt. All these events take place with the span of a few seconds. Most distributed systems are very complex. For example, in the above case the branch computers must perform as stand-alone machine while simultaneously interacting with other machines in the network and share data as well.
ADVANTAGES AND DISADVANTAGES OF DISTRIBUTED SYSTEMS There are both advantages and disadvantages for distributed processing. Advantages The advantages of distributed processing include: Local control of local data The major benefit from a distributed data processing system is local control of local data. This means that the organization can take more responsibility for developing, scheduling, introducing, and managing applications. Above all, a local perspective can keep the information system more focused on the local organization’s objectives.
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Lower cost Often the hardware in a distributed system is less expensive than that for a centralized system. Several minicomputers or microcomputers cost less than one mainframe. The maintenance costs of these machines are also less compared to the centralized system’s machines. Modularity Distributed systems tend to e modular. As the demand for processing increases, most micros, minis and other supportive equipment such as secondary storage devices and printers can be added to the network. For example, in a local area network (LAN), when a new microcomputer needs to be added it is simply plugged into the system and within minutes it is a functioning part of the existing network. Better response times When only one centralized computer is used, the response time to a user’s request can be delayed as more and more users make demands on the system. But in distributed system, local processing is done on local machines, and in many systems, local machines only occasionally need to call, upon the resources of the response time as more users are added to a distributed system. Ability to share data Another advantage of a distributed system is its ability to share data across the nodes in a network. Without a network, it is difficult or impossible to share data. Of course, the floppy disk from one machine can be taken to another, and the data can be shared in this way; but it is much more convenient if the machines can share data through the electronic interface of a network. Greater reliability Still another advantages of distributed systems is their reliability. If the centralized system breaks down, the whole operations of the organizations will to come to a halt. Networks, in general, are not subject to such catastrophes. If one computer in the network breaks down, the rest of the machines may not be affected depending on the network topology. Direct user interaction Another advantages is that users directly interact with the information system in distributed processing. This means that users will not consider the computer an unapproachable, mysterious black box located behind closed doors. Disadvantages Disadvantages networks have disadvantages, too, and these must be consider before a system is decentralized. They include: Technical problems of connecting dissimilar machines Technical problems can sometimes be overwhelming for a distributed system. Additional layers of operating system software are needed to translate and coordinate the flow of data
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between machines. Sometimes a link between mainframes and microcomputers can be difficult to establish. Need for sophisticate communication systems Distributed processing requires the development of a data communication system. These systems can e costly to develop and use. In addition, their maintenance can be a costly affair. Data integrity and security problems Because data maintained by distributed systems can be accessed at many locations in the network, controlling the integrity of a database can be difficult. Lack of professional support Finally, distributed computers are often place in locations where little or no data processing is available. Consequently, they will be run nonprofessionals. Another aspect is that the communication systems also require highly trained personnel for their maintenance.
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UNIT-IV OFFICE ATUOMATION
3:0 INTRODUCTION Microsoft Access is a powerful program to create and manage your databases. It has many built in features to assist you in constructing and viewing your information. Access is much more involved and is a more genuine database application than other programs such as Microsoft Works. 3:1 OBJECTIVES First of all you need to understand how Microsoft Access breaks down a database. Some keywords involved in this process are: Database File, Table, Record, Field, Data-type.
3:2Starting Microsoft Access •
Two Ways 1. Double click on the Microsoft Access icon on the desktop.
2. Click on Start --> Programs --> Microsoft Access
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3:3 Creating New, and Opening Existing Databases
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The above picture gives you the option to: •
Create a New Database from scratch
•
Use the wizard to create a New Database
•
Open an existing database o
The white box gives you the most recent databases you have used. If you do not see the one you had created, choose the More Files option and hit OK. Otherwise choose the database you had previously used and click OK.
3:4Create a database using the Database Wizard 1. When Microsoft Access first starts up, a dialog box is automatically displayed with options to create a new database or open an existing one. If this dialog box is displayed, click Access Database Wizards, pages, and projects and then click OK.
If you have already opened a database or closed the dialog box that displays when Microsoft Access starts up, click New Database on the toolbar.
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2. On the Databases tab, double-click the icon for the kind of database you want to create. 3. Specify a name and location for the database. 4. Click Create to start defining your new database
3:5Create a database without using the Database Wizard 1. When Microsoft Access first starts up, a dialog box is automatically displayed with options to create a new database or open an existing one. If this dialog box is displayed, click Blank Access Database, and then click OK.
If you have already opened a database or closed the dialog box that displays when Microsoft Access starts up, click New Database on the toolbar, and then double-click the Blank Database icon on the General tab. 2. Specify a name and location for the database and click Create. (Below is the screen that shows up following this step)
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3:6 Tables A table is a collection of data about a specific topic, such as students or contacts. Using a separate table for each topic means that you store that data only once, which makes your database more efficient, and reduces data-entry errors.
Tables organize data into columns (called fields) and rows (called records).
3:7Create a Table from scratch in Design view 1. If you haven't already done so, switch to the Database Window You can press F11 to switch to the Database window from any other window.
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2. Double-Click on "Create table in Design view". (DESIGN VIEW)
3. Define each of the fields in your table.
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Under the Field Name column, enter the categories of your table.
o
Under Data Type column, enter the type you want for you categories.
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The attribute of a variable or field that determines what kind of data it can hold. For example, in a Microsoft Access database, the Text and Memo field data types allow the field to store either text or numbers, but the Number data type will allow the field to store numbers only. Number data type fields store numerical data that will be used in mathematical calculations. Use the Currency data type to display or calculate currency values. Other data types are Date/Time, Yes/No, Auto Number, and OLE object (Picture). o
Under the Description column, enter the text that describes what you field is. (This field is optional).
o
For our tutorial enter the following items:
3:8Primary Key •
One or more fields (columns) whose value or values uniquely identify each record in a table. A primary key does not allow Null values and must always have a unique value. A primary key is used to relate a table to foreign keys in other tables.
•
NOTE: You do not have to define a primary key, but it's usually a good idea. If you don't define a primary key, Microsoft Access asks you if you would like to create one when you save the table.
•
For our tutorial, make the Soc Sec # field the primary key, meaning that every student has a social security number and no 2 are the same. o
To do this, simply select the Soc Sec # field and select the primary key button
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After you do this, Save the table
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3:9Switching Views •
To switch views form the datasheet (spreadsheet view) and the design view, simply click the button in the top-left hand corner of the Access program.
Datasheet View
Design View
Displays the view, which allows you to Displays the view, which allows you to enter fields, enter raw data into your database
data-types, and descriptions into your database
table.
table.
3:10Entering Data •
Click on the Datasheet View and simply start "chugging" away by entering the data into each field. NOTE: Before starting a new record, the Soc Sec # field must have something in it, because it is the Primary Key. If you did not set a Primary Key then it is OK.
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3:11Manipulating Data •
Adding a new row o
•
Simply drop down to a new line and enter the information
Updating a record o
Simply select the record and field you want to update, and change its data with what you want
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Deleting a record o
Simply select the entire row and hit the Delete Key on the keyboard
3:12Advanced Table Features w/Microsoft Access •
Assigning a field a specific set of characters o
Example) Making a Social Security Number only allows 9 characters. 1. Switch to Design View
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2. Select the field you want to alter 3. At the bottom select the General Tab
4. Select Field Size 5. Enter the number of characters you want this field to have •
Formatting a field to look a specific way (HINT: You do not need to assign a field a specific set of characters if you do this) o
Example) Formatting Phone Number w/ Area Code (xxx) xxx-xxxx 1. Switch to Design View 2. Select the field you want to format 3. At the bottom select the General Tab 4. Select Input Mask Box and click on the ... button at the right. 5. Select Phone Number option
6. Click on Next 7. Leave !(999) 000-0000 the way it is. This is a default. 8. Click Next
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9. Select which option you want it to look like 10. Click Next 11. Click Finish •
Selecting a value from a dropdown box with a set of values that you assign to it. This saves you from typing it in each time o
Example)Choosing a city that is either Auburn, Bay City, Flint, Midland, or Saginaw 1. Switch to Design View 2. Select the field you want to alter (City) 3. At the bottom select the Lookup Tab 4. In the Display Control box, select Combo Box 5. Under Row Source Type, select Value List 6. Under Row Source, enter the values how you want them displayed, separated by a comma. (Auburn, Bay City, Flint, Midland, Saginaw) NOTE:This will not alphabetize them for you, so you will have to do that yourself. It should look something like this:
7. Select in the datasheet view and you should see the change when you go to the city field.
3:13Relationships
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After you've set up multiple tables in your Microsoft Access database, you need a way of telling Access how to bring that information back together again. The first step in this process is to define relationships between your tables. After you've done that, you can create queries, forms, and reports to display information from several tables at once.
A relationship works by matching data in key fields - usually a field with the same name in both tables. In most cases, these matching fields are the primary key from one table, which provides a unique identifier for each record, and a foreign key in the other table. For example, teachers can be associated with the students they're responsible for by creating a relationship between the teacher's table and the student's table using the TeacherID fields.
Having met the criteria above, follow these steps for creating relationships between tables. 1. In the database window view, at the top, click on Tools ---> Relationships 2. Select the Tables you want to link together, by clicking on them and selecting the Add Button 3. Drag the primary key of the Parent table (Teacher in this case), and drop it into the same field in the Child table (Student in this case.)
4. Select Enforce Referential Integrity
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When the Cascade Update Related Fields check box is set, changing a primary key value in the primary table automatically updates the matching value in all related records.
o
When the Cascade Delete Related Records check box is set, deleting a record in the primary table deletes any related records in the related table
5. Click Create and Save the Relationship
3:14Forms A form is nothing more than a graphical representation of a table. You can add, update, delete records in your table by using a form. NOTE: Although a form can be named different from a table, they both still manipulate the same information and the same exact data. Hence, if you change a record in a form, it will be changed in the table also.
A form is very good to use when you have numerous fields in a table. This way you can see all the fields in one screen, whereas if you were in the table view (datasheet) you would have to keep scrolling to get the field you desire.
3:15Create a Form using the Wizard It is a very good idea to create a form using the wizard, unless you are an advanced user
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and know what you are doing. Microsoft Access does a very good job of creating a form using the wizard. The following steps are needed to create a basic form: 1. Switch to the Database Window. You can do this by pressing F11 on the keyboard. 2. Click on the Forms button under Objects on the left side of screen 3. Double click on Create Form Using Wizard 4. On the next screen select the fields you want to view on your form. Most of the time you would select all of them. 5. Click Next 6. Select the layout you wish 7. Click Next 8. Select the style you desire...HINT: if you plan on printing your form, I suggest you use a light background to save on printer toner and ink 9. Click Next 10. Give you form a name, and select Open the Form and enter information 11. Select Finish 12. You should see your form. To adjust the design of your form, simply hit the design button (same as with the tables), and adjust your form accordingly 3:16Reports A report is an effective way to present your data in a printed format. Because you have control over the size and appearance of everything on a report, you can display the information the way you want to see it. 3:17Create a Report using the Wizard As with the Form, it is a very good idea to create a report using the wizard, unless you are an advanced user. Microsoft Access does a very good job using the wizard to create reports. 1. Switch to the Database Window. You can do this by pressing F11 on the keyboard. 2. Click on the Reports button under Objects on the left side of screen 3. Double click on Create Report Using Wizard 4. On the next screen select the fields you want to view on your form. Most of the time you would select all of them.
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5. Click Next 6. Select if you would like to group your files. Keep repeating this step for as many groupings as you would like. 7. Click Next 8. Select the layout and the paper orientation you desire 9. Click Next 10. Select the style you desire...HINT: if you plan on printing your report, I suggest you use a light background to save on printer toner and ink 11. Click Next 12. Give you report a name, and select Preview the Report 13. Select Finish 14. You should see your report. To adjust the design of your report, simply hit the design button (same as with the tables), and adjust your report accordingly
3:18Creating Mail Merge Labels using a Wizard Microsoft Access lets you create Mailing Labels for your database that you have. To do this do the following: 1. Switch to the Database Window. You can do this by pressing F11 on the keyboard. 2. Click on the Reports button under Objects on the left side of screen 3. Click on New
4. Select Label Wizard and the table you would like to get your information from.
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