C OMPUTING

COMPUTING

COMPUTING

ESSENTIALS

ESSENTIALS

199920001999200019992000

Presentations by:Fred Bounds

Timothy J. O’Leary Linda I. O’Leary

55Secondary StorageSecondary Storage

CHAPTER

3Computing Essentials 1999 - 2000 Chapter Five

Competencies

After reading this chapter, you should be able to:

1. Describe today’s standard floppy disk and compare it to Zip, SuperDisks and HiFD disks.

2. Describe the following kinds of disks: internal hard disks, hard-disk cartridges and hard-disk packs.


Competencies

3. Describe ways to improve hard-disk operations: disk caching, redundant arrays of inexpensive disks and data compression.

4. Compare the CD and DVD optical disk formats.


Competencies

5. Describe the different types of optical disks.

6. Describe magnetic tape streamers and magnetic tape reels.


Overview

• Computers permanently save information– For future use– To share information with others– To modify information already available

• Stores programs and data

• As opposed to temporary storage (RAM), which is volatile, secondary storage is nonvolatile

Floppy Disks

Floppy disks are removable storage media. Today’s standard is 1.44 MB. Tomorrow’s might be a Zip, SuperDisk or HiFD. Data is recorded on tracks and sectors.


Floppy Disks

• Removable storage media inserted into disk drives

• Flat circular pieces of mylar plastic rotating within a jacket

• The bits of data are represented by the presence or absence of magnetic charges


Floppy Disks - Today’s Standard

• Storage capacities range from 360 KB to 1.44 MB

• Jackets covering the mylar disk can be flexible or sturdy

• Write-protect notch or window to prevent inadvertent erasure or write-over


Floppy Disks - Tomorrow’s Standard

• Zip Disks– 100 MB capacity (70 times regular floppy)– Becoming standard feature on new systems– May be the next floppy disk standard

• SuperDisks– 120 MB capacity– Can read and write standard floppies, while

Zips cannot


Floppy Disks - Tomorrow’s Standard

• HiFD disks– 200 MB capacity (140 times

standard floppy)– Can also read and write

standard floppies


The Parts of a Floppy Disk

• Data recorded in rings called called tracks

• Tracks divided into wedge-shaped sections called sectors

• Most disks manufactured without tracks and sectors and must have “soft sectors” added through the formatting process


Typical Floppy Disk Capacities

DDeessccrriippttiioonn CCaappaacciittyy

Zip 100 MB

HiFD 200 MB

DDeessccrriippttiioonn CCaappaacciittyy

Zip 100 MB

HiFD 200 MB

2HD 1.44 MB

SuperDisk 120 MB


read-write headread-write head

access armaccess arm

3 1/2-inch floppy disk

3 1/2-inch floppy disk

tracks (invisible)tracks (invisible)

How a Disk Drive Works

• Drive motor turns mylar disk

• Access arm moves read-write heads back and forth

• Read-write heads then read or write on the disk surface

Hard Disks

Hard disks are of three types: internal hard disk, hard-disk cartridge and hard-disk pack.


Hard Disks

• Composed of metallic rather than plastic disks

• Fast information storage and retrieval

• Read-write heads “fly” over the disk surface on a cushion of extremely thin air


Hard Disks

• A smoke particle, human hair or fingerprint could cause a head crash

• Head crashes occur when the read-write head contacts the disk surface


Materials that Materials that can cause a can cause a head crashhead crash





human hair

human hair

dust particle

dust particle

fingerprintfingerprint

smoke particlesmoke particle


Internal Hard Disk

• Located inside the system unit

• Also known as fixed disk

• For storing the operating system, other programs and large data files


Internal Hard Disk

• One or more metallic platters sealed inside a container

• Container holds– Motor for rotating the

disks– Access arm and read-

write heads


Internal Hard Disk

• Advantages over floppy disks– Capacity (up to

thousands times a single floppy

– Speed (ten times the speed)


Hard-Disk Cartridges

• Hard disk can be easily removed

• Give microcomputer fast access to large amounts of data


Hard-Disk Cartridges

• Complements internal hard disk

• Typical capacity, 2 GB

• Popular vendors: Iomega and SyQuest


Hard-Disk Packs

• Removable, massive storage capacity

• Common in mainframe systems

• Composed of a larger number of platters, resembling a stack of record albums


Hard-Disk Packs

• Most platters offer read-write surfaces on top and bottom

• Used with larger computer systems


Hard-Disk Packs

• Access time - time between the computer’s request for data from secondary storage and the completion of the data transfer


Performance Enhancements

• Disk caching – Uses hardware and software to anticipate

data needs – Frequently used data is stored in memory,

when needed, the access time is much faster



• Redundant arrays of inexpensive disks (RAID)– Groups of low cost hard-disk drives

grouped together using networks and special software

– Performs as a single large-capacity disk– But faster than a single disk of comparable

size



• File compression and decompression– Increase storage capacity– Reduce space required for storage– Aids in file transmission– WinZip and PKZip are well-known

programs

Optical Disks

Optical disks use laser technology. CD and DVD are optical disk formats.


• Compact, high capacity form of permanent storage

• Laser beam writes by creating a pattern of pits (holes) and lands (flat areas) to encode data bits

• Laser beams reflect off the pits and lands to read the data

Optical Disks


Optical Disks

• Up to 4.7 gigabytes of data

• Equivalent of over 1 million typewritten pages

• Three types of optical discs CD-ROM, CD-R and erasable optical discs, or CD-RW


CD-ROM

• Stands for compact disc-read-only memory

• Can be read from, but not written to

• Can hold up to 650 MB of information– Grolier Electronic Encyclopedia - nine

million words and 1900 pictures– Used to distribute large software packages


How a CD-How a CD-ROM ROM worksworks

How a CD-How a CD-ROM ROM worksworks

CD-ROMCD-ROMCD-ROMCD-ROM

CD-ROM carrying CD-ROM carrying casecase

CD-ROM carrying CD-ROM carrying casecase

CD-ROM driveCD-ROM driveCD-ROM driveCD-ROM drive

Reflected lightReflected lightReflected lightReflected light

Reflecting surfaceReflecting surfaceReflecting surfaceReflecting surface

Laser beamLaser beamLaser beamLaser beam


CD-R

• Stands for CD-Recordable• Also known as WORM, or write once,

read many• Ideal for use as permanent data archives

for essential company information• CD changers or CD jukeboxes can

facilitate rapid access to large amounts of information


• Also known as rewritable optical discs• Unlike CD-R, these discs can be written

on numerous times• Most common technology is magneto-

optical (MO) disc drive, combining magnetic and optical technologies

• Capacities up to 1,000 megabytes (a gigabyte)

CD-RW


Digital Versatile Disk

• Commonly known as digital video disk or DVD

• Up to 4.7 gigabytes capacity, seven times CD

• With two-sided storage, 17 gigabytes out soon

• Predicted to replace CD as a standard


Digital Versatile Disk

• DVD-ROM - provide high quality, movie length videos

• DVD-R - consumer recordable version just getting started

• DVD-RAM or DVD-RW - rewritable version

Magnetic Tape

Magnetic tape streamers and magnetic tape reels are used primarily for backup purposes.


Magnetic Tape

• Disks offer fast, direct access to data programs

• Tapes are sequential access, because they have to be fast forwarded or rewound before a specific location can be reached


• A common sequential access method of permanent storage method

• A common form of data backup in companies with larger computer systems

Magnetic Tape


• Two forms of tape storage – Magnetic tape streamers– Magnetic tape reels

Magnetic Tape


• Backup tape cartridge units used with microcomputer systems

• Typical capacities range from 120 MB to 5 GB

• Advanced forms use digital audio tape (DAT)

Magnetic Tape Streamers


Magnetic Tape Reels

• Used with minicomputer and mainframe computers

• Often 1/2 inch wide and 1/2 mile long

• Stores 1600 to 6400 characters per inch

• Tapes are run on magnetic tape drives or magnetic tape units


Magnetic Tape Reels

Take-up reelTake-up reelTake-up reelTake-up reel

Read-write headRead-write headRead-write headRead-write head

Supply reelSupply reelSupply reelSupply reel

Erase headErase headErase headErase head

TapeTapeTapeTape

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