Main memory
External Storage
CS 21 - Computer Organization and Assembly Language Programming Lecture 6 Memory: Main Memory and Storage
University of the Philippines - Diliman College of Engineering Department of Computer Science
Optical Disks
Main memory
Outline
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Main memory
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External Storage
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Optical Disks
External Storage
Optical Disks
Main memory
Outline
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Main memory
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External Storage
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Optical Disks
External Storage
Optical Disks
Main memory
External Storage
Optical Disks
Main memory
memory that is between the cache and the External Memory outside the CPU, but still in the mainboard/motherboard usually comes in modular packages implemented using semiconductor technology
Main memory
External Storage
Semiconductor Memory
Types of Semiconductor Memory: RAM ROM EPROM Flash memory
Optical Disks
Main memory
External Storage
RAM: Random Access Memory Characteristics of Random Access Memory: almost exclusively the choice for Main memory in modern computer systems �Randomly� Accessible(what does this mean?) Read-write type Data is volatile Could either be Static or Dynamic
Optical Disks
Main memory
External Storage
ROM: Read Only Memory Characteristics of Read Only Memory: like RAM, ”Randomly” Accessible Read-Only type Data is non-volatile
Optical Disks
Main memory
External Storage
Optical Disks
EPROM: Erasable Programmable Read Only Memory Characteristics of Erasable Programmable Read Only Memory: like RAM, �Randomly� Accessible Read and write capability, but could only be written on in special conditions Writing could be facilitated via UV light, or via electrical means Data is non-volatile
Main memory
External Storage
Flash Memory Characteristics of Flash Memory: like RAM, �Randomly� Accessible Read and write capability usually uses USB interface increase in capacity makes it a challenger for External Memories
Optical Disks
Main memory
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Optical Disks
Main memory
External Storage
External Storage
lowest in the memory hierarchy largest in capacity, lowest in speed most common are magnetic and optical disks
Optical Disks
Main memory
External Storage
Optical Disks
Magnetic Disks commonly known as Hard Disk Drives data is stored in platters attached to a central spindle platters are coated with magnetizable material head or heads modify the orientation of magnetized particles on the platters
Main memory
Magnetic Disks
External Storage
Optical Disks
Main memory
External Storage
Magnetic Disks
data on a platter is organized into concentric circles called tracks one track is divided into sectors, where data is stored
Optical Disks
Main memory
External Storage
Optical Disks
Magnetic Disks
Disk access time depends on three factors: Seek time: the time it takes for the disk arm to move the heads to the right position/cylinder. (5 15 msec) Rotational Latency: the time it takes for the platter to rotate the starting sector under the head. (typical hard disks rotate around 5400rpm) Transfer time: the time during which the sectors, in one track, are read by the head. (5 20 MB/sec)
Main memory
External Storage
Optical Disks
Magnetic Disks
Most of the data in the world exists in magnetic disks! How about crashes?
Main memory
External Storage
Optical Disks
Magnetic Disks
We cope with crashes, technical glitches, and limited disk lifespan with
Main memory
External Storage
Optical Disks
Magnetic Disks
We cope with crashes, technical glitches, and limited disk lifespan with DATA REDUNDANCY
Main memory
External Storage
Data Redundancy
Individual users: backup with optical media.
Optical Disks
Main memory
External Storage
Data Redundancy
Individual users: backup with optical media.
Optical Disks
Main memory
External Storage
Data Redundancy
Individual users: use cloud computing/storage.
Optical Disks
Main memory
External Storage
Data Redundancy
Individual users: use cloud computing/storage.
Optical Disks
Main memory
External Storage
Data Redundancy: RAID
Businesses/Corporate Entities: RAID.
Optical Disks
Main memory
External Storage
Data Redundancy: RAID
Businesses/Corporate Entities: RAID. RAID stands for Redundant Array of Inexpensive Disks several disks appear as a single disk to the user there are several kinds of RAID, identified by number
Optical Disks
Main memory
External Storage
Data Redundancy: RAID 0 RAID 0.
Optical Disks
Main memory
External Storage
Data Redundancy: RAID 0 RAID 0. data is striped across several disks multiple disks appear as one, capacities add up dude, where’s the redundancy?
Optical Disks
Main memory
External Storage
Data Redundancy: RAID 1
RAID 1.
Optical Disks
Main memory
External Storage
Data Redundancy: RAID 1
RAID 1. shadowing or mirroring of data failure of single disk transparent to users
Optical Disks
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Optical Disks
Main memory
External Storage
Optical Disks most common form of secondary storage in use today used in data back-ups very cheap key enabler: LASER technology in most cases: Read-only, could only be written on once
Optical Disks
Main memory
External Storage
Optical Disks
Optical Disks data is WRITTEN by a powerful laser creating microscopic indentations(pits) in CD data is READ by shining a another laser in the disk and sensing the reflected light pits and lands placed on the disk in a spiral when unwound, spiral would reach 5.6 km!
Main memory
External Storage
Optical Disks
Optical Disks How about DVDs? the physical disc is actually the same key difference is in laser frequence used(0.65nm from 0.78nm) smaller pits (0.4 microns to 0.8 microns) tighter spiral (0.74 microns between track compared to 1.6 microns per track)
Main memory
External Storage
Optical Disks
How about DVDs? result? more data! (4.7GB from 650MB) Dibidi! Dibidi!
Optical Disks
Main memory
External Storage
Optical Disks
What is the main problem with optical disks?
Optical Disks
Main memory
External Storage
Optical Disks
What is the main problem with optical disks? too accessible = prone to damage
Optical Disks
Main memory
External Storage
Optical Disks
What is the main problem with optical disks? too accessible = prone to damage Solution? Error Correction Codes/ECC
Optical Disks
Main memory
External Storage
Optical Disks
Optical Disks Error Correction Codes key concept: in a word or byte, we can deduce a damaged bit using the remaining undamaged ones enables SOME tolerance for scratched or damaged disc surfaces knowing this, how should you clean your CDs and DVDs?