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Another si gnificant devel op ment i n third-generati on co mputers i ncl uded the use of an operati ng syste m which all owed machi nes to run many different progra ms at once w ith a central progra m which monitored and co-ordi nated the co mputer ’ s me mory.

Fourth Generation (1971-Present): Use of Microprocessors The fourth generati on co mputers can be characterized by the use of m icro processors, a si ngle silicon chi p on which thousands of i ntegrated circui -ts were built. The use of M icroprocessors consi derabl y reduced the size. Now co mputers fit i nthe pal mof the hand. The personal co mputers andl aptops all made use of m icroprocessors. For the first ti mei n 1981, I BMi ntroduced co mputers for the ho me users, and i n 1984 Apple i ntroduced the Maci ntosh. The fourth generati on co mputers beca me very powerful, nowthey coul d be li nked together to for ma net work. Thel aptops, ho me PC ’ s, pal mtops, mobile phones all can be attri butedtofourth generati on co mputers that we use today.

Fifth Generation (Present and Beyond): Artificial Intelligence This categorizati on of co mputer generati ons is based uponthe use of artifici al i ntelli gence. It is still i n the devel op ment phase. However, so me robots have been devel oped which are hel pi ngi n medical science andresearch. So me of the co mputer applicati ons li ke voice recogniti on, text to speech and speechtotext can be attri buted to fifth generati on co mputers. The movies li ke Ter m i nator series (1, 2 and 3) and Robot are based on the concept of fifth generati on co mputers.

1.4 HARDWARE 1.4.1 Input Devices

An i nput device is a peri pheral device which accepts data or co mmands and sends it to the CPU . There are different types of data to be sent to CPU . Dependi ng upon the data type the i nput devices are used. For exa mple barcode reader is used to the read bar-codes. The i nput devices are used to convert the data obtai ned i nto the l anguage which co mputer understandsi. e. co mputer ’ s owni nternal code before sendi ng it to the CPU . So me of the Input devices are expl ai ned as foll ows:

Keyboard

is the most co mmonl y used i nput devi ce t hat converts al phabets, nu mbers, and other speci al characters i nt o el ectri cal pul ses whi ch can be

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understood by the co mputers. The most popul ar keyboard used today is the 101-keys Q WERTY keyboard, called as the standard keyboard. The types of keys on a keyboard are: – Nu meric/Di git keys e. g. 1, 2, 3, 4 – Al phabetic keys/Letter keys e. g. A , B , C , Dandso on. There are 26letters of English al phabet – Functi on keys e. g. F1, F2, F3, F4 and so on. – Punct uati on keys e. g. :, ; , (), ’ – Speci al character keys e. g. < , > , ?, × , |, \, @ , #, ^ etc. Most of these keys are pri nted when used al ong w ith the Shift key. – Non-pri ntable control keys e. g. Enter/Ret urn key, Space key, Caps Lock,

Shift key, arrowkeys, Tab key( moves cursor tothe next tabstop), Delete key.

Mouse

is a s mall hand hel d device which is used to i ndicate a positi on or move ment on a co mputer ’ s displ ay screen by rolli ng it over a mouse pad. Mouse enters datai nt wo different ways. Firstl y, asthe mouse is moved, a ball underneath it or a l aser bea mli ght revol ves and this move ment is detected by sensors which send the data to the CPU . Secondl y, a mouse generall y has a left click button and a ri ght click button. A mouse is of 3 types: Mechanical mouse, Optical mouse and Opto mechanical mouse. Also they can be cl assifiedi nter ms of connecti vitytothe co mputerli ke w ired and w ireless mouse.

Track Ball :

Atrackball has a ball ontopthat canrotate freel y. Instead of movi ng the deviceli ke a mouse, one can si mpl y roll the ball w ith the fi ngers to move the poi nter.

Touchpad:

A touchpad (or trackpad) is a poi nti ng device that can transl ate the moti on and positi on of a user ’ s fi ngers to a rel ati ve positi on on scree n. Touchpads are a co m mon feat ure of l apto p, notebook co mputers.

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Joystick:

Aj oystick consists of a s mall lever whichis moved bythe user to control move ment on ascreen. Inthis case also sensors detect the move ment of the lever and send the correspondi ng data to the CPU . These are generall y used for pl ayi ng vi deo ga mes.

Light Pen:

It is a poi nti ng device that utilizes a li ght-sensiti ve detector toselect objects on a displ ay screen. It is si m il ar to a mouse, except that w ith a li ght pen you can move the poi nter and select ob jects on the displ ay screen by directl y poi nti ng to the objects w ith the pen.

Touch Screen:

It is speci all y desi gned vi deo displ ay screen that has the capability to recei ve i nput fro mthe touch of a fi nger. Digitizing Tablet: Di gi ti zi ng Ta bl et / D i gitizers refers to an electronic pl astic board on whichspecifyi ng al ocati oncorrespondstol ocati on onthe co mputer screen . These are used by architects and engi neersi n Co mputer Ai ded Desi gni ng( CAD) for desi gni ng purposes.

Bar Code Readers:Bar Code Reader (BCR)

is a photoelectricscannerthat transl atesthe bar codesi nto di gital code. Bar Codes are speci al i dentificati oncodes pri ntedas aset of vertical stri pped marks of different w i dth usuall y seen on manufact ured retail products. The bar code i dentifies the product to the super market’ s co mputer, which has a descri pti ons and the l atest price of the product.

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Optical Character Recognition (OCR):

It is the electronic transl ati on of pri nted i mages or nu merals, letters or sy mbols which may be hand written or typedi nto di gital code. It i nvol vestransl ati ngthetext fro mpaperi ntoa for mthat the co mputer can mani pul ate and feedit directl yi nto co mputer file. It is w i del y used to convert books and docu ments i nto electronic files.

Optical Mark Reader (OMR):

It refers to a device that reads pencil marks and converts the mi nto a for mthat can be processed by a co mputer.

Magnetic Ink Character Reader (MICR):

MI CR is a character recogniti on technol ogy used pri maril y by the banki ngi ndustry to facilitate the processi ng of cheques. It consists of speci al i nk called magnetic i nk that is used to write characters on the check and deposit for ms to be processed by an MI CR .

Microphone:

M icrophone is a voice recogniti on device that converts audi o si gnals to electrical waves and these can be converted by electronic circuitry i n the co mputer to di gital fro m . The user can si mpl y i nstruct the co mputer about thetaskto be perfor med w iththe hel p of a m icrophone. It can be usedto recordsound or to co mmunicate w ith another co mputer user vi atheInternet. Many co mputers co me w ith built-i n m icrophones.

Digital Camera:

Di gital ca meras all owtotake di gital photographs. Thei mages are stored on a me mory chi p or disk that can be transferred to the co mputer.

Web Camera:

A webca m or web ca mera is a ca mera that generates i mages that can be accessed on the Internet. Many people use webca ms for chatti ng, vi deo conferenci ng etc. Webca mall ows usertotakei mages fro mthe co mputer and co mmunicate visuall y w ith other users on the Internet.

Scanner/Image Scanner:

It is a devicethat converts photos, dra w i ngs, graphics andtext i nto di gital for mas i nput tothe co mputer. It hel ps i n preservi ng paper docu ments i n electronic for mso that it does not deteri orate w ith age and can be displ ayed or pri nted whenever required. It stores the docu ment as i mage. These storedi mages can be altered and mani pul atedi ni nteresti ng ways if the co mputer hasi mage-processi ngsoft ware. There are 2types ofi mage scanners:

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(a) Hand-held scanners:

These scanners are hel di n hand to scan ani mage or docu ment by movi ng it over the object. These are portable.

(b) Flat-bed scanners:

These scanners have a fl at gl ass surface where the docu ment is pl acedj ust li ke i n a Xerox copier. The li d of the scanner is cl osed before gi vi ng the co mmand for scanni ng. Fl at- bed Hand- hel d Fl at- bed scanners are the co mmonl y used scanners i n everyday life.

1.4.2 Output devices

Output devices are usedto convert the machi ne codes recei vedfro mthe CPU i nto a for m which can be understood by the users i. e. hu mans. The output generated by output devices may be of 2 types: 1. Soft copy output 2. Hard copy output Afe w of the output devices are discussed bel ow :

Monitor:

A monitor is a displ ay device which shows the data recei ved fro m co mputeri nreadable and understand able for mtothe users i. e. hu man, onto a vi deo screen. Monitors vary greatl y i n size and i n resol uti on (cl arity of graphics). There are 3 co mmon types of monitor:

VGA ( Vi deo Graphics Array): 640 × 400 pi xels. SVGA ( Super Vi deo Graphics Array): 800 × 600 pi xels. EVGA or XVGA ( Extended Vi deo Graphics Array): 1024 × 768 pi xels.

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The first co mputer monitors used cathode ray t ubes ( CRT). Modern monitors use li qui d crystal displ ay ( TFT- LCD) or Li ght Em itti ng Di ode ( LED) displ ay. The mai n advantages of LCDs over CRT displ ays are that LCDs consu me less power, take up much less space, are consi derabl y li ghter, and reduces eye strai n. ( ) is a vari ant of li qui d Thin film transistor liquid crystal displaycrystal displ ay i mproves i mage quality. TFT-LCD The quality of monitor depends upon:

(i) Resolution :

It refers to the nu mber of pi xels i n a unit sq. area. It shows thesharpness andcl arity ofi mage. Moretheresol uti on, hi gherthe quality of monitors.

(ii) Refresh rate :

It refers to the nu mber of ti mes the monitor is refreshed i n a unit second. It is measuredi n hertz .

(iii) Dot pitch :

It refers to the distance bet ween 2 pi xels. At ti mes monitors also act as i nput devices e. g. use of touch screen monitors. PRINTERS Pri nters are used to pri nt the output data on a paper. Such output is referred to as pri ntout or hard copy.

Types of Printers

Impact Printers I mpact pri nters refertothose pri nters wheretext ori mageis pri nted bystri ki ng ha mmers or pi ns agai nst a ri bbon. These pri nters have mechanis msi m il ar to a type writer. These pri nters are now dryi ng out and are bei ng repl aced by the non-i mpact pri nters. These are of t wo types.

Character Printer Onl y one character at a ti me is pri nted. It has rel ati vel y sl ower speed. E . g. Dot Matri x Pri nter.

Line Printer These pri nters are capable of pri nti ng an entireli ne at oneti me. Afast li ne pri nt er can pri nt as many as 3, 000 li nes per m i nute. The disadvantages of these are that they cannot pri nt graphics, the pri nt qualityis l ow , andthey are very noisy.

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Non-Impact Printers Non-I mpact pri nters are used al most every where now . These are faster and quieterthani mpact pri nters. These pri nters provi de better quality of output. Two types of non-i mpact pri nters often used arel aser pri nters andi nk-jet pri nters.

Character Printer:

It pri nts onl y one character at ati me. It has rel ati vel y sl ower speed. E . g. Dot matri x pri nter

Pri nter

I mpact Non-I mpact

Character Pri nterDot Matri x Li ne Pri nter

Character Pri nter-Ink-Jet Page Pri nter Laser

Dot Matrix Printer Dot matri x pri nter is very popul ar pri nter. It pri nts the text and graphics w ith the hel p of an array of metal pi ns whichis known as pri nthead. This pri nthead stri kes ani nked ri bbon to pri nt dots on the paper which for ms the character onthe paper as a result one character is pri nted at a ti mei nthis ki nd of pri nt er. The quality of pri nt depends on the nu mber of pi ns usedi n the pri nthea d, which may varyfro m9to 24. Dot- matri x pri nters pri nt about 50-500 characters per second (cps).

Laser Printer This type of pri nter uses l aser bea mto produce text or i mage on dru m . When the l aser li ght hits the dru m , then li ght modifies the electrical charge on the dru m . A reservoir of toner then rolls the dru m , which is picked up by the charged porti ons of the dru m . After that, the co mbi nati on of heat and pressure transfers the toner to the paper. Copy machi nes, also worki nthesa me way. Laser pri nters areso meti mes called page pri nters. Its speed ranges fro m about 4 to 20 pages of text per m i nute (pp m ). Atypical rate of 6 pp mis equi valent to about 40 characters per second (cps). It has i n- built RAMchi ps to store docu ments output fro mthe co mputer. Al ot of RAMis used while worki ng i n desktop publishi ng and pri nti ng co m plicated docu ments w ith col our and many graphics. It also has ROMchi ps to store fonts andits own s mall dedicated processor.

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Ink-Jet Printer Ink-Jet pri nter is very popul ar as it is i nexpensi ve and also offers the facility of col our pri nti ng. It has nozzles havi ng veryfi ne holes, whichpri ntsthe characters by sprayi ng patterns of i nk on the paper. The i nk co mes out of the nozzle i n for mof vapours. It for ms the desiredletter or shape at the desired pl ace after passi ng through a reflecti ng pl ate. Ink-jet pri nteris sl oweri nspeed which pri nts around 4 pages of text per m i nute (pp m ). It pri ntsi n aso me whatl ower resol uti on(300-720 dpi) thanl aser pri nters. So me ne w , expensi vei nk-jet pri nters pri nt up 1200 or 1400 dpi. A vari ati on on i nk-jet technol ogyis the bubble-jet pri nter. It uses m i ni at ure heati ng ele ments to force speci all y for mul ated i nks through pri nt heads w ith 128 ti ny nozzles. This technol ogy is co mmonl y usedi n portable pri nters.

Plotters It is a speci al output device that is desi gnedto produce sharp quality andl arge sized graphics, dra w i ngs, mapsi n different col our sche mes. They are generall y used for desi gni ng applicati ons where hi gh quality graphic output on l arge sheet of paper is required. These devices have beco me less popul ar over the years, but still produce hi gh-quality dra w i ngs. There are 2 types of pl otters:

( a (b ) Dru mpl otters

) Fl atbed pl otters

Sound Systems/Speakers These arethe output devices which output sound or audi oi nthefor mof speech and music. These output devices have i mportant i mplicati ons for their use by visuall y i mpaired people because to operate co mputers they rel y heavil y on sound syste ms.

Peri pheral devices: All devices connectedtothe ports of co mputer are called Peri pheral devices. They can be i nput devices, output devices and storage devices.

Storage Devices These devices are usedto store data or progra ms. These devices are non-vol a tile. These can be either i nternall y built i ntothe co mputer or can be externally attached to the co mputer vi a USB port. A Hard disk dri ve is co mmonl y used storage device and can be either external ori nternal. Othersi ncl ude pen dri ve, fl oppy disk, me mory card reader etc.

Vol atile me moryisthe onei n whichthe contents( data or progra ms) stored on the storage medi u mgets erased off once the power suppl y to the co mputer is s w itched off. Non-vol atile me mory is j ust the opposite.

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