1. Presentations by: Fred Bounds
Timothy J. O’Leary Linda I. O’Leary
COMPUTING
ESSENTIALS
1999
2000
1999
Presentations by: Fred Bounds
2000

2. 5
CHAPTER
Secondary Storage

3. Computing 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.
Computing Essentials Chapter Five

4. Computing Essentials 1999 - 2000 Chapter Five
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.
Computing Essentials Chapter Five

5. Computing Essentials 1999 - 2000 Chapter Five
Competencies
5. Describe the different types of optical disks.
6. Describe magnetic tape streamers and magnetic tape reels.
Computing Essentials Chapter Five

6. Computing Essentials 1999 - 2000 Chapter Five
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
Computing Essentials Chapter Five

7. 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.

8. Computing Essentials 1999 - 2000 Chapter Five
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
Computing Essentials Chapter Five

9. 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
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10. 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
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11. Floppy Disks - Tomorrow’s Standard
HiFD disks
200 MB capacity (140 times standard floppy)
Can also read and write standard floppies
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12. 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
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13. Typical Floppy Disk Capacities
2HD 1.44 MB
SuperDisk 120 MB
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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
read-write head
access arm
3 1/2-inch floppy disk
tracks (invisible)
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15. Hard Disks
Hard disks are of three types: internal hard disk, hard-disk cartridge and hard-disk pack.

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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
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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
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18. Materials that can cause a head crash
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19. Materials that can cause a head crash
dust particle
human hair
fingerprint
smoke particle
Materials that can cause a head crash
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Internal Hard Disk
Located inside the system unit
Also known as fixed disk
For storing the operating system, other programs and large data files
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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
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Internal Hard Disk
Advantages over floppy disks
Capacity (up to thousands times a single floppy
Speed (ten times the speed)
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Hard-Disk Cartridges
Hard disk can be easily removed
Give microcomputer fast access to large amounts of data
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Hard-Disk Cartridges
Complements internal hard disk
Typical capacity, 2 GB
Popular vendors: Iomega and SyQuest
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Hard-Disk Packs
Removable, massive storage capacity
Common in mainframe systems
Composed of a larger number of platters, resembling a stack of record albums
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Hard-Disk Packs
Most platters offer read-write surfaces on top and bottom
Used with larger computer systems
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Hard-Disk Packs
Access time - time between the computer’s request for data from secondary storage and the completion of the data transfer
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28. 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
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29. Performance Enhancements
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
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30. Performance Enhancements
File compression and decompression
Increase storage capacity
Reduce space required for storage
Aids in file transmission
WinZip and PKZip are well-known programs
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31. Optical Disks
Optical disks use laser technology. CD and DVD are optical disk formats.

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Optical Disks
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
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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
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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
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CD-ROM drive
CD-ROM
How a CD-ROM works
CD-ROM carrying case
Reflected light
Laser beam
Reflecting surface
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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
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CD-RW
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)
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38. 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
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39. 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
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40. Magnetic Tape
Magnetic tape streamers and magnetic tape reels are used primarily for backup purposes.

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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
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Magnetic Tape
A common sequential access method of permanent storage method
A common form of data backup in companies with larger computer systems
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Magnetic Tape
Two forms of tape storage
Magnetic tape streamers
Magnetic tape reels
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44. Magnetic Tape Streamers
Backup tape cartridge units used with microcomputer systems
Typical capacities range from 120 MB to 5 GB
Advanced forms use digital audio tape (DAT)
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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
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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
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Magnetic Tape Reels
Take-up reel
Supply reel
Read-write head
Erase head
Tape
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