meljun cortes computer information processing chapter5

7/31/2019 MELJUN CORTES Computer Information Processing Chapter5

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CHAPTER 5: STORAGE

OBJECTIVES

After completing this chapter, students will be able to:

Identify various types of storage media and storage devices

Explain how data is stored on a floppy disk

Understand how to care for a floppy disk

Describe how a hard disk organizes data

List the advantages of using disks

Explain how data is stored on compact discs

Understand how to care for a compact disc

Differentiate between CD-ROMs and DVD-ROMs

Identify uses of tapes, PC Cards, smart cards, microfilm, and microfiche

CHAPTER OVERVIEW

This chapter explains various storage media and storage devices. Students discover howmemory is different from storage. Floppy disks are introduced, and characteristics of a floppy

disk, floppy disk drives, care of floppy disks, and high-capacity floppy disks are presented.

Hard disks are explained, and students find out about characteristics of a hard disk, how a hard

disk works, removable hard disks, hard disk controllers, RAID, and maintaining data on a hard

disk. Compact discs, including CD-ROMs and DVD-ROMs, are described. Finally, students

learn about tapes, PC Cards, and other types of storage such as smart cards, microfilm and

microfiche, enterprise storage systems, and data warehouses.

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CHAPTER 5 : STORAGE CCT101

5.1 Memory

While performing a processing operation, the CPU needs a place to temporarily

hold instructions to be executed and data to be used with those instructions.Memory, which is composed of one or more chips on the motherboard, holds dataand instructions while they are being processed by the CPU.

The two basic types of memory are volatile and non-volatile. The contents ofvolatile memory, such as RAM, are lost (erased) when the power to the computeris turned off. The contents ofnon-volatile memory, however, are not lost whenpower is removed from the computer. For example, once instructions have beenrecorded onto a non-volatile ROM chip, they usually cannot be erased or changed,and the contents of the chip are not erased when power is turned off.

5.2 Storage

Storage, also called secondary storage, auxiliary storage, or mas storage, holdsitems such as data, instructions, and information for future use. Think of storagea filing cabinet used to hold file folders, and memory as the top of your desk.When you need to work with a file, you remove it from the filing cabinet (storage)and place it on your desk (memory). When you are finished with the file, youreturn it to the filing cabinet (storage).

Storage is non-volatile, which means that items in storage are retained even whenpower is removed from the computer. A storage medium (media is the plural) isthe physical material on which items are kept. One commonly used storagemedium is a disk, which is a round, flat piece of plastic or metal with a magnetic

coating on which items can be written. A storage device is the mechanism used torecord and retrieve items to and from a storage medium.

Storage devices can function as sources of input and output. For example, eachtime a storage device transfers data, instructions, and information from a storagemedium into memory - a process called reading - it functions as an input source.When a storage device transfers these items from memory to a storage medium -a process called writing - it functions as an output source.

The speed of a storage device is defined by its access time, which is the minimumtime it takes the device to locate a single item on a disk. Compared to memory,storage devices are slow. The access time of memory devices is measured innanoseconds (billionths of a second), while the access time of storage devices ismeasured in milliseconds (thousandths of a second).

The size, or capacity, of a storage device, is measured by the number of bytes(characters) it can hold. Figure 5-1, lists the terms used to define the capacity ofstorage devices. For example, a typical floppy disk can store 1.4 MB of data(approximately 1,440,00 bytes) and a typical hard disk can store 8 GB of data(approximately 8,000,000,00 bytes).

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CCT101 CHAPTER 5 : STORAGE

Figure 5-1 the capacity of a storage device is measured by the number of bytes it can

hold.

Storage requirements among users vary greatly. Users of smaller computers, suchas small business users, might need to store a relatively small amount of data. Forexample, a field sales representative might have a list of names, addresses, andtelephone numbers of 50 customers, which he or she uses on a daily basis. Such alist might require no more than several thousand bytes of storage. Users of largercomputers, such as banks, libraries, or insurance companies, process data formillions of customers and thus might need to store trillions of bytes worth ofhistorical or financial records in their archives.

To meet the needs of a wide range of users, numerous types of storage media andstorage devices exist. Figure 5-2 shows how different types of storage media andmemory compare in terms of relative cost and speed. The storage media includedin the pyramid are discussed in this chapter.

Figure 5-2 this pyramid shows how

different types of storage media and

memory compare in terms of relative cost

and speed. Memory is faster than storage,

but expensive and not practical for al

storage requirements. Storage is les

expensive but is slower than memory.

5.3 FLOPPY DISKS

A floppy disk, or diskette, is a portable, inexpensive storage medium that consistsof a thin, circular, flexible plastic disk with a magnetic coating enclosed in asquare-shaped plastic shell. In the early 1970s, IBM introduced the floppy disk asa new type of storage. Because these early 8-inch wide disks had flexible plasticcovers, many users referred to them as floppies. The next generation of floppieslooked much the same, but were only 5.25-inches wide.

Today, the most widely used floppy disk is 3.5-inches wide. The flexible cover of

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the earlier floppy disks has been replaced with a rigid plastic outer cover. Thus,although todays 3.5-inch disks are not at all floppy, the term floppy disk still isused.

As noted, a floppy disk is a portable storage medium. When discussing a storage

medium, the term portable means you can remove the medium from one computerand carry it to another computer. For example, you can insert a floppy disk intoand remove it from a floppy disk drive on many types of computers. A floppydisk drive is a device that can read from and write to a floppy disk.

Characteristics of Magnetic Media

A floppy disk is a type of magnetic media, which means it uses magneticpatterns to store items such as data, instructions, and information on thedisks surface. Most magnetic disks are read/write storage media; that is,you can access (read) data from and place (write) data on a magnetic diskany number of times, just as you can with an audiocassette tape.

A new, blank floppy disk has nothing stored on it. Before you can write ona new floppy disk, it must be formatted. Formatting is the process ofpreparing a disk (floppy disk or hard disk) for reading and writing byorganizing the disk into storage locations called tracks and sectors (Figure5-3). A track is a narrow recording band that forms a full circle on thesurface of the disk. The disks storage locations then are divided into pie-shaped sections, which break the tracks into small arcs called sectors. Asector is capable of holding 512 bytes of data. A typical floppy disk storesdata on both sides and has 80 tracks on each side of the recording surfacewith 18 sectors per track.

Sometimes, a sector is damaged or has a flaw and cannot store data. Asector that cannot be used due to a physical flaw on the disk is called a badsector. When you format a disk, the operating system marks these badsectors as unusable. If a sector that contains data is damaged, you may beable to use special software to recover the data.

For reading and writing purposes, sectors are grouped into clusters. Acluster consists of two to eight sectors (the number varies depending onthe operating system). A cluster is the smallest unit of space used to storedata. Even if a file consists of only a few bytes, an entire cluster is used forstorage. Although each cluster holds data from only one file, one file canbe stored in many clusters.

A storage capacity are determined the density of the disk. A higherdensity means that the disk has a larger storage capacity. Disk density iscomputed by multiplying together the number of sides on the disk, thenumber of tracks on the disk, the number of sectors per track, and thenumber of bytes in a sector. For example, for a typical 3.5-inch floppydisk, disk density is computed as follows: 2 (sides) x 80 (tracks) x 18(sectors per track) x 512 (bytes per sector) = 1,474,560 bytes, orapproximately 1.4 MB.

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If you are using the Windows operating system, the formatting processalso defines the file allocation table (FAT), which is a table of informationused to locate files on a disk. The FAT is like a library card catalogue foryour disk that contains a listing of al files, file types, and locations. If youformat a disk that already contains data, instructions, or information, the

formatting process erases the file location information and redefines thefile allocation table for these items. The actual files on the disk, however,are not erased. For this reason, if you accidentally format a disk, you oftencan unformatit with special software.

FIGURE 5-3 a track is a narrow recording band that forms a ful circle on the

surface of the disk. The disks storage locations then are divided into pie-shaped

sections, which break the tracks into small arcs called sectors. A sector is

capable of holding 512 bytes of data.

Characteristics of a Floppy Disk

To protect them from accidentally being erased, floppy disks have a write-protect notch. A write-protect notch is a small opening in the corner of thefloppy disk with a tab that you slide to cover or expose the notch. Thewrite-protect notch works much like the recording tab on a VHS tape: ifthe recording tab is removed, a VCR cannot record onto the VHS tape.

On a floppy disk, if the write-protect notch is exposed, or open, the drivecannot write on the floppy disk. If the write-protect notch is covered, orclosed, the drive can write on the floppy disk. The write-protect notch onlyaffects the floppy disk drives capability of writing on the disk; a floppydisk drive can read from a floppy disk whether the write-protect notch is

open or closed. Some floppy disks have a second opening on the oppositeside of the disk that does not have the small tab; this opening identifies thedisk as a high-density floppy disk.

Most floppy disks are pre-formatted by the disks manufacturer. If youmust format a floppy disk yourself, you do so by issuing a formattingcommand to the operating system. Because PC-compatible computersusing the Windows operating system format floppy disks differently thanMacintosh computers, a Macintosh computer cannot use a PC formattedfloppy disk without special equipment or software. A disk drive such asthe Apple Macintosh Super-Drive, however, can read from and write on

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both Macintosh and PC formatted floppy disks.

Floppy Disk Drives

As noted, a floppy disk drive (FDD) is a device that can read from andwrite on a floppy disk. Desktop personal computers usually have a floppydisk drive installed inside the system unit. Many laptop computers haveremovable floppy disk drives that can be replaced with other types ofdrives or devices, or they use an external floppy disk drive that plugs intothe laptop.

If a computer has one floppy disk drive, the drive usually is designateddrive A; if the computer has two floppy disk drives, the second one usuallyis designated drive B. To read from or write on a floppy disk, a floppy diskdrive must support that floppy disks density. That is, to use a high-densityfloppy disk, you must have a high-density floppy disk drive. Floppy disk

drives are downward compatible, which means they recognize and can useearlier media. Floppy disk drives are not upward compatible, however,which means they cannot recognize newer media. For example, a lower-density floppy disk drive cannot read from or write on a high-densityfloppy disk.

On any 3.5-inch floppy disk, a piece of metal called the shutter covers anopening in the rigid plastic shell. When you insert a floppy disk into afloppy disk drive, the drive slides the shutter to the side to expose aportion of both sides of the floppy disks recording surface.

The read/write head is the mechanism that actually reads items from or

writes items on the floppy disk. Figure 5-4 illustrates the steps for readingfrom and writing on a floppy disk. The average access time for currentfloppy disk drives to locate an item on the disk is 84 ins, or approximately1/12 of a second.

On the front of most floppy disk drives is a light emitting diode (LED) thatlights up when the drive is accessing the floppy disk. You should notremove a floppy disk when the floppy disk drive is accessing the disk.

Sometimes, a floppy disk drive will malfunction when it is attempting toaccess a floppy disk and will display an error message on the computersmonitor screen. If the same error occurs with multiple floppy disks, the

read/write heads in the floppy disk drive may have a build-up of dust ordirt. In this case, you can try cleaning the read/write heads using a floppydisk cleaning kit.

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Figure 5-4 how a floppy disk drive works

How Do You Care for a Floppy Disk?

With reasonable care, floppy disks can last at least seven years - providingan inexpensive and reliable form of storage. When handling a floppy disk,you should avoid exposing it to heat, cold, magnetic fields, andcontaminants such as dust, smoke, or salt air. Exposure to any of theseelements could damage or destroy the data, instructions, and informationstored on the floppy disk.

High-Capacity Floppy Disks

Several manufacturers have high-capacity floppy disk drives that use disks

with capacities of 10 MB and greater. With these high-capacity disks,you can store large files containing graphics, audio, or video; transport a

large number of files from one computer to another; or make a backup of

al of your important files. A back up is duplicated of a file, program, ordisk that can be used if the original is lost, damaged or destroy

A SuperDiskTM

drive is a high-capacity disk drive developed by Jmation

that reads from and writes on a 120 MB SuperDiskTM

floppy disk. SonyElectronics Inc. has developed HiFD

TM(High-Capacity FD), a high-

capacity floppy disk drive that reads from and writes on a 20 MBHiFD

Mfloppy disk. Both the SuperDisk

TMdrive and the HiFD

Mdrive are

downward compatible; that is, they can read from and write on standard3.5-inch floppy disks as wel as their own high-capacity disks.

Another type of high-capacity disk drive is the Zip drive. A Zip drive

is a special high-capacity disk drive developed by Iomega Corporation.Zip drives use a 3.5-inch Zip disk, which is slightly larger than and

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about twice as thick as a 3.5-inch floppy disk, and can store 250 MB of

data - equivalent to about 70 high-density floppy disks. Today, many newcomputers are equipped with a built-in Zip drive, so that using Zip

disks to store and transport large files is as easy as storing smaller files on

a standard floppy disk. You also can use an external Zip drive with a

desktop or laptop.

5.4 HARD DISKS

When personal computers were introduced, software programs and their relatedfiles required small amounts of storage and fit easily on floppy disks. As softwarebecame more complex and included graphical user interfaces and multimedia, filesizes and storage requirements increased. Today, hard disks - which provide farlarger storage capacities and much faster access times than floppy disks - are oneof the primary media for storing software programs and files. Current personalcomputer hard disks can store from 4 to 50 GB of data, instructions, and

information.

A hard disk usually consists of several inflexible, circular disks, called platters, onwhich items are stored electronically. A platter in a hard disk is made ofaluminium, glass, or ceramic and is coated with a material that allows items to bemagnetically recorded on its surface. On hard disks, the platters, the read/writeheads, and the mechanism for moving the heads across the surface of the disk areenclosed in an airtight, sealed case that protects the platters from contamination.The hard disk in most desktop personal computers is housed inside the systemunit. Such hard disks, which are not portable, are considered fixed disks. Harddisks also can be removable. Removable hard disks are discussed later in thischapter.

Characteristics of a Hard Disk

Like a floppy disk, a hard disk is a type of magnetic media that storesitems using magnetic patterns. Hard disks also are read/write storagemedia; that is, you can both read from and write on a hard disk anynumber of times. Hard disks undergo two formatting steps, and possibly athird process, called partitioning. The first format, called a low-levelformat, organizes both sides of each platter into tracks and sectors todefine where items will be stored on the disk. Because a hard disk oftenhas some bad sectors, the hard disk manufacturer usually performs thelow-level format.

After low-level formatting is complete, the hard disk can be divided intoseparate areas called partitions by issuing a special operating systemcommand. Each partition functions as if it were a separate hard disk drive.Partitioning often is performed to make hard disks more efficient (faster)or to allow you to install multiple operating systems on the same harddisk.

If a hard disk has only one partition, the hard disk usually is called, ordesignated, drive C. If the hard disk is divided into two partitions, the first

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partition is designated drive C and the second partition is designated driveD, and so on. Unless specifically requested by the consumer, mostmanufacturers define a single partition (drive C) on the hard disk.

After low-level formatting and partitioning, a high-level format command

is issued through the operating system to define, among other items, thefile allocation table (FAT) for each partition. Recall that the FAT is a tableof information used to locate files on a disk. As with the low-level format,most hard disk manufacturers perform the high-level format for theconsumer. You can partition a hard disk yourself using special operatingsystem commands. You then must issue a high-level format command foreach partition.

How a Hard Disk Works

Most hard disks have multiple platters stacked on top of one another and

each platter has two read/write heads, one for each side. The hard disk has

arms that move the read/write heads to the proper location on the platter(Figure 5-5).

Because of the stacked arrangement of the platters, the location of theread-write head often is referred to by it cylinder instead of its track.

Figure 5-5 how a hard

disk works

A cylinder is the location of a single track through al platters (Figure 5-6).

For example, if a hard disk has four platters (eight sides), each with 1,00tracks, then it will have 1,00 cylinders with each cylinder consisting ofeight tracks (two for each platter). While your computer is running, theplatters in the hard disk rotate at a high rate of speed, usually 5,40 to7,20 revolutions per minute. The platters continue spinning until power isremoved from the computer.

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Figure 5-6 acylinderis the location of a single track through al platters on a hard

disk.

The spinning motion creates a cushion of air between the platter and itsread/write head so the read/write head floats above the platter instead ofmaking direct contact with the platter surface. The distance between theread/write head and the platter is approximately two millionths of an inch.

As shown in Figure 5-7, this close clearance leaves no room for any typeof contamination. If contamination is introduced, t the hard disk can havea head crash. A head crash occurs when a read/write head touches c thesurface of a platter, usually resulting in a los of data or sometimes los ofthe entire drive. Todays hard disks are built to withstand shocks and aresealed tightly to keep out contaminants, which means head crashes are leslikely to occur.

Access time for todays hard disks ranges from five to elevenmilliseconds. Access time for a hard disk is significantly faster than for afloppy disk for two reasons: (1) a hard disk spins much faster than afloppy disk and (2) a hard disk spins constantly, while a floppy disk startsspinning only when it receives a read or write command.

Figure 5-7, because the gap

between a disk read/write

head and the platter is so

small, contaminants such as a

smoke particle, dust particle,

or human hair could render

the drive unusable.

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Some computers are able to improve the hard disk access time by using

disk caching. Disk cache is a portion of memory that the CPU uses to store

frequently accessed items. Disk cache works similarly to memory cache.

When a program needs data, instructions, or information, the CPU checksthe disk cache. If the item is located in disk cache, the CPU uses that item

and completes the process. If the CPU does not find the requested item inthe disk cache, then the CPU must wait for the hard disk drive to locateand transfer the item from the disk to the CPU.

Some disk caching systems also attempt to predict what data, instructions,or information might be needed next and place them into cache beforethey are requested. Because disk caching significantly improves diskaccess times, almost al new disk drives work with some amount of diskcache.

Maintaining Data Stored on a Hard Disk

Most manufacturers guarantee their hard disks to last somewhere betweenthree and five years, although many last much longer with proper care. Toprevent the los of items stored on a hard disk, you should performpreventative maintenance such as deframenting or scanning the disk forerrors. Operating systems such as Windows provide many maintenanceand monitoring utilities.

5.5 COMPACT DISCS

In the past, when you purchased off-the-shelf software, you received one or morefloppy disks that contained the files needed to install or run the software program.

As software programs became more and more complex, the number of floppydisks required to store the programs increased, sometimes exceeding thirty disks.These more complex programs required a larger storage medium, which is whymany of todays software programs are distributed on compact discs.

A compact disc (CD) is a flat, round, portable, metal storage medium that usuallyis 4.75 inches in diameter and les than one-twentieth of an inch thick (Figure 5-8). Compact disks store items such as data, instructions, and information by usingmicroscopic pits (indentations) and land (flat areas) that are in the middle layer ofthe disc. (Most manufacturers place a silk-screened label on the top layer of thedisc so you can identify it.) A high-powered laser light creates the pits. A lower-powered laser light reads items from the compact disc by reflecting light through

the bottom of the disc, which usually is either solid gold or silver in color. Thereflected light is converted into a series of bits that the computer can process.Land causes light to reflect, which is read as binary digit 1. Pits absorb the light;this absence of light is read as binary digit 0.

A compact disc stores items in a single track that spirals from the center of thedisc to the edge of the disc. As with a hard disk, this single track is divided intoevenly sized sectors in which items are stored.

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Figure 5-8 how a leaser reads data on a compact disc

5.5.1 Different Types of Compact Discs?

Two basic types of compact discs designed for use with computers are aCD-ROM and DVD-ROM. Just about every personal computer todayincludes a CD-ROM or DVD-ROM drive, which are devices that can readcompact discs, including audio CDs. A desktop personal computertypically has a CD-ROM or DVD-ROM drive installed in a drive bay; onmany laptop computers, these drives are removable so they can bereplaced with other types of drives or devices.

Recall that a floppy disk drive is designated as drive A. The drivedesignation of a CD-ROM or DVD-ROM drive usually follows

alphabetically after that of the hard disk. For example, if your hard disk isdrive C, then the compact disc is drive D.

On most of these drives, you push a button to slide out a tray, insert yourcompact disc with the label side up, and then push the same button toclose the tray. Other convenient features on most of these drives include avolume control button and a headphone jack so you can use stereoheadphones to listen to audio.

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CD-ROMs

A CD-ROM (pronounced SEE-DEE-Rom, which is anabbreviation for compact disc read-only memory) is a silver-colored compact disc that uses the same laser technology as audio

CDs for recording music. Unlike an audio CD, a CD-ROM cancontain text, graphics, and video, as well as sound. The contents ofstandard CD-ROMs are written, or recorded, by the manufacturerand only can be read and used. That is, they cannot be erased ormodified-hence, the name read-only.

For a computer to read items on a CD-ROM, you must place it intoa CD-ROM drive or CD-ROM player. Because audio CDs andCD-ROMs use the same laser technology, you also can use yourCD-ROM drive to listen to an audio CD while working on yourcomputer.

A CD-ROM can hold up to 70 MB of data, instructions, andinformation, or about 450 times that which can be stored on a high-density 3.5-inch floppy disk. Because CD-ROMs have such highstorage capacities, they are used to store and distribute todayscomplex software. Some programs even require that the disc be inthe drive each time you use the program.

CD-R (compact disc-recordable)

Is a technology that allows you to write on a compact disc usingyour own computers Whereas the discs manufacturer records thedata, instructions, and information on a standard CD-ROM, you

record your own items such as text, graphics, and audio, onto aCD-R (compact disc-recordable). You can write on the disc instages - writing on part of it one time and writing on another part ata later time. You can, however, write on each part only once andyou cannot erase it.

Once you have recorded the CD-R, you can read from it as manytimes as you wish. In order to write on a CD-R, you must haveCD-R software and a CD-R drive. A CD-R drive can read andwrite both audio CDs and standard CD-ROMs with read speeds ofup to 24X and write speeds of up to 8X. Manufacturers often listthe write speed first, for example, as 8/24. While CD-R drives are

somewhat more expensive than standard CD-ROM drives, theirprice continues to drop and many computers today are equippedwith CD-R drives.

CD-RW (compact disc-rewriteable)

Is an erasable disc that you can write on multiple times CD-RWovercomes one of the disadvantages of CD-R disks - that you canwrite on them only once. With CD-RW, the disc acts like a floppyor hard disk, allowing you to write and rewrite data, instructions,and information onto it multiple times. To write on a CD-RW disc,you must have CD-RW software and a CD-RW drive. The read

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speed of these drives is up to 32X, write speed up to 8X, andrewrite speed up to 4X. One problem with CD-RW is that thesediscs cannot be read by al CD-ROM drives.

DVD-ROMs

Although CD-ROMs have huge storage capacities, even a CD-ROM is not large enough for many of todays complex programs.Some software, for example, is sold on five or more CD-ROMs.To meet these tremendous storage requirements, some softwaremoved from CD-ROMs to the larger DVD-ROM format - atechnology that can be used to store video items, such as motionpictures. A DVD-ROM (digital video disc-ROM) is an extremelyhigh capacity compact disc capable of storing from 4.7 GB to 17GB - more than enough to hold a telephone book containing everyresident in the United States. Not only is the storage capacity of a

DVD-ROM greater than a CD-ROM, a DVD-ROMs quality alsofar surpasses that of a CD-ROM. In order to read a DVD-ROM,you must have a DVD-ROM drive or DVD player. These driveshave speeds up to 40X and can read most types of CD-ROMs.

At a glance, a DVD-ROM looks just like a CD-ROM. Althoughthe size and shape are similar, a DVD-ROM stores data,instructions, and information in a slightly different manner andthus achieves a higher storage capacity. A DVD-ROM uses one ofthre storage techniques. The first technique involves making thedisc more dense by packing the pits closer together. A secondtechnique involves using two layers of pits. For this technique to

work, the lower layer of pits is semitransparent so the laser canread through it to the upper layer. This technique doubles thecapacity of the disc. Finally, some DVD-ROMs are double-sided,which means you must remove the DVD-ROM and turn it over toread the other side. The storage capacities of various types ofDVD-ROMs are shown in the table in Figure 5-9.

Figure 5-9 storage capacities of DVD-ROMs.

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5.6 TAPES

One of the first storage media used with mainframe computers was magnetic tape,a magnetically coated ribbon of plastic capable of storing large amounts of data

and information at a low cost. Tape storage requires sequential access, whichrefers to reading or writing data consecutively. Like a music tape, you mustforward or rewind the tape to a specific point to access a specific piece of data.

For example, to access item W, you must pas sequentially through points Athrough V. Floppy disks, hard disks, and compact discs al use direct access, orrandom access, which means you can locate a particular data item or fileimmediately, without having to move consecutively through items stored in frontof the desired data item or file. Because sequential access is much slower thandirect access, tapes are no longer used as a primary method of storage. Instead,tapes are used most often for long-term storage and backup.

Similar to a tape recorder, a tape drive is used to read from and write data andinformation onto a tape. Although older computers used reel-to-reel tape drives,todays tape drives use tape cartridges. A tape cartridge is a small, rectangular,plastic housing for tape. Tape cartridges containing one-quarter-inch wide tapeare slightly larger than audiocassette tapes and frequently are used for personalcomputer backup.

Some personal computers have permanently mounted tape drives, while othershave external units. On larger computers, tape cartridges are mounted in aseparate cabinet. Three common types of tape drives are QIC, DAT, and DLT,which is the fastest and most expensive of the three. The table in Figure 5-10summarizes each of these tapes.

Figure 5-10 summarizes each of these tapes.

5.7 PC CARDS

A PC Card is a thin, credit card-sized device that fits into a PC Card expansionslot on a laptop or other personal computer. Different types and sizes of PC Cardsare used to ad storage, additional memory, communications, and soundcapabilities to a computer. PC Cards most often are used with laptops and otherportable computers.

PC Cards are available in three types, which are designated Type I, Type II, and

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Type III. The thicker Type II cards are used to house hard disks and currentlyhave storage capacities of more than 520 MB (Figure 5-11). The advantage of aPC Card hard disk is portability; that is, you easily can transport large amounts ofdata, instructions, and information from one machine to another. Type I and TypeI cards, used to ad memory or communications capabilities to a computer, are

discussed in other chapters.

Some digital cameras also use a matchbook-size card, sometimes called a picturecard or compact flash card, to store pictures, which are then transferred to acomputer by inserting the card into a card reader or slot. These compact flashcards have storage capacities ranging from 2 MB to 256MB.

Figure 5-1 this type II PC Card is a hard

disk with 1 GB of storage space.

5.8 OTHER TYPES OF STORAGE

Although the majority of data, instructions, and information are stored on floppydisk, hard disk, compact disc, tape, and PC Cards, other more specialized meansfor storing these items also are used. These include smart cards and microfilm and

microfiche. Each of these media is discussed in the following sections.

5.8.1 Smart Cards

A smart card, which is similar in size to a credit card or ATM card, stores

data on a thin microprocessor embedded in the card (Figure 5-12). Two

types of smart cards exist: intelligent and memory. An intelligent smart

card contains a CPU and has input, process, output, and storagecapabilities. In contrast, a memory card has only storage capabilities.

When the smart card is inserted into a specialized card reader, the

information on the smart card is read and, if necessary, updated.

One popular use of smart cards is to store a prepaid dollar amount, as in a prepaid

telephone calling card. You receive the card with a specific dollar amount storedin the microprocessor. Each time you use the card, the available amount of

money is reduced. Using these cards provides convenience to the caller,

eliminates the telephone companys need to collect coins from telephones, andreduces vandalism of pay telephones. Other uses of smart cards include storing

patient records, vaccination data, and other health-care information; trackinginformation such as customer purchases or employee attendance; and storing aprepaid amount, such as electronic money.

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Figure 5-12 many hotels issue smart cards instead of keys to hotel guests. With the smart

card, guests gain access to their rooms as well as hotel services such as cafeterias,

swimming pools, lockers, and parking lots.

5.8.2 Microfilm and Microfiche

Microfilm and microfiche are used to store microscopic images ofdocuments on roll or sheet film. Microfilm uses a 100- to 215-foot rol offilm. Microfiche uses a small sheet of film, usually about four inches bysix inches. The images are recorded onto the film using a device called a

computer output microfilm (COM) recorder. The stored images are sosmall they can be read only with a microfilm or microfiche reader.

Applications of microfilm and microfiche are widespread. Libraries usethese media to store back issues of newspapers, magazines, and genealogyrecords. Large organizations use microfilm and microfiche to archiveinactive files. Banks, for example, use it to store transactions andcancelled checks, and the U.S. Army uses it to store personnel records.Using microfilm and microfiche provides a number of advantages: itgreatly reduces the amount of paper firms must handle; it is inexpensive;and it has the longest life of any storage medium.

meljun cortes computer information processing chapter5

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