capron 8 ppt 06

Copyright © 2003 by Prentice HallCopyright © 2003 by Prentice Hall

Computers:Computers:Tools for an Information AgeTools for an Information Age

Chapter 6Chapter 6Storage and Multimedia: Storage and Multimedia:

The Facts and MoreThe Facts and More

22 Copyright © 2003 by Prentice HallCopyright © 2003 by Prentice Hall

ObjectivesObjectives

List the benefits of secondary storageList the benefits of secondary storageIdentify and describe storage media that Identify and describe storage media that are available for personal computersare available for personal computersDifferentiate among the principal types of Differentiate among the principal types of secondary storagesecondary storageDescribe how data is stored on a diskDescribe how data is stored on a diskDiscuss the benefits of multimediaDiscuss the benefits of multimediaExplain how data is organized, accessed, Explain how data is organized, accessed, and processedand processed


Secondary StorageSecondary Storage

Separate from the computer itselfSeparate from the computer itself

Software and data stored on a Software and data stored on a semipermanent basissemipermanent basis Unlike memory, not lost when power is lostUnlike memory, not lost when power is lost

BenefitsBenefits


Magnetic Disk StorageMagnetic Disk Storage

Data represented as magnetized spots on Data represented as magnetized spots on surface of spinning disksurface of spinning disk Spots on disk converted to electrical impulsesSpots on disk converted to electrical impulses

Primary typesPrimary types DiskettesDiskettes Hard DisksHard Disks


Reading/Writing DataReading/Writing Data

Access arm moves read/write Access arm moves read/write head over particular locationhead over particular location

Read/write head hovers a few Read/write head hovers a few millionths of an inch above millionths of an inch above platterplatter

If head touches platter, a head If head touches platter, a head crash occurs and data is crash occurs and data is destroyeddestroyed

Data can be destroyed if head Data can be destroyed if head touches miniscule foreign matter touches miniscule foreign matter on surface of diskon surface of disk


Disk PacksDisk Packs

Each platter has its own Each platter has its own access arm with access arm with read/write headread/write head

Most disk packs Most disk packs combine platters, access combine platters, access arms, and read/write arms, and read/write headhead


Hard Disks for Personal ComputersHard Disks for Personal Computers

Sealed modules that mount in a 3 Sealed modules that mount in a 3 ½” bay½” bay

Capacity in gigabytesCapacity in gigabytes

Accessing files much faster than Accessing files much faster than accessing files on diskettesaccessing files on diskettes

Some contain removable Some contain removable cartridgescartridges Iomega’s Jaz drive is very popularIomega’s Jaz drive is very popular


Redundant Array of Independent Redundant Array of Independent Disks (RAID)Disks (RAID)

A group of disks that work A group of disks that work together as onetogether as one Raid level 0 spreads data from a Raid level 0 spreads data from a

single file over several drivessingle file over several drivesCalled data stripingCalled data striping

Increases performanceIncreases performance Raid level 1 duplicates data on Raid level 1 duplicates data on

several drivesseveral drivesCalled disk mirroringCalled disk mirroring

Increases fault toleranceIncreases fault tolerance


How Data Is OrganizedHow Data Is Organized

TrackTrack

SectorSector

ClusterCluster

CylinderCylinder


Disk Access SpeedDisk Access Speed

Access time - the time needed to access Access time - the time needed to access data on diskdata on disk

Three factorsThree factors Seek timeSeek time Head switchingHead switching Rotational delayRotational delay

Once data found, next step is Once data found, next step is data transferdata transfer


Optical Disk StorageOptical Disk Storage

Provides inexpensive and compact storage with Provides inexpensive and compact storage with greater capacitygreater capacityLaser scans disk and picks up light reflections Laser scans disk and picks up light reflections from disk surfacefrom disk surfaceCategorized by read/write capabilityCategorized by read/write capability Read-only media - user can read from, but not write to Read-only media - user can read from, but not write to

diskdisk Write-once, read-many (WORM) - user can write to Write-once, read-many (WORM) - user can write to

disk oncedisk once Magneto-optical - combines magnetic and optical Magneto-optical - combines magnetic and optical

capabilitiescapabilities


Compact DisksCompact Disks

CD-ROM - drive can only read data CD-ROM - drive can only read data from CDsfrom CDs

CD-ROM stores up to 700 MB per diskCD-ROM stores up to 700 MB per disk Primary medium for software distributionPrimary medium for software distribution

CD-R - drive can write to disk onceCD-R - drive can write to disk once Disk can be read by CD-ROM or CD-R Disk can be read by CD-ROM or CD-R

drivedrive

CD-RW - drive can erase and record CD-RW - drive can erase and record over data multiple timesover data multiple times

Some compatibility problems trying to Some compatibility problems trying to read CD-RW disks on CD-ROM drivesread CD-RW disks on CD-ROM drives


Digital Versatile Disk (DVD)Digital Versatile Disk (DVD)

Short wavelength laser can read densely Short wavelength laser can read densely packed spotspacked spots DVD drive can read CD-ROMsDVD drive can read CD-ROMs Capacity up to 17GBCapacity up to 17GB Allows for full-length moviesAllows for full-length movies Sound is better than on audio CDsSound is better than on audio CDs

Several versions of writable and rewritable Several versions of writable and rewritable DVDs existDVDs exist


MultimediaMultimedia

Presents information with text, illustrations, Presents information with text, illustrations, photos, narration, music, animation, and photos, narration, music, animation, and film clipsfilm clips

Not practical until the advent of the optical Not practical until the advent of the optical diskdisk

RequirementsRequirements

ApplicationsApplications


Magnetic Tape StorageMagnetic Tape Storage

Tape similar to tape used in Tape similar to tape used in music cassettesmusic cassettes

Categorized in terms of densityCategorized in terms of density Number of bits per inch stored on Number of bits per inch stored on

tapetape

Used primarily for backup of data Used primarily for backup of data stored on disk systemsstored on disk systems


Backup SystemsBackup Systems

Imperative to have copies of important data Imperative to have copies of important data stored away from the computerstored away from the computer Disks occasionally failDisks occasionally fail Software installation can cause computer to crashSoftware installation can cause computer to crash Users make mistakes entering dataUsers make mistakes entering data

Tape is ideal backup mediumTape is ideal backup medium Can copy entire hard disk to single tape in minutesCan copy entire hard disk to single tape in minutes Backup can be scheduled when you are not going to Backup can be scheduled when you are not going to

use the systemuse the system


Organizing and Accessing Stored Organizing and Accessing Stored DataData

CharacterCharacter

FieldField

RecordRecord

FileFile

DatabaseDatabase


File Plan OverviewFile Plan Overview

Must devise a plan for placing data on a Must devise a plan for placing data on a storage unitstorage unit

Key factorsKey factors Whether users must access data directly Whether users must access data directly

(immediately)(immediately) How data must be organized on diskHow data must be organized on disk Type of processing that will take placeType of processing that will take place


File OrganizationFile Organization

Three major methods of organizing data Three major methods of organizing data files in secondary storagefiles in secondary storage SequentialSequential DirectDirect IndexedIndexed


Hashing AlgorithmHashing Algorithm

Applies mathematical formula to key to Applies mathematical formula to key to determine disk address of given recorddetermine disk address of given record Collision occurs when hashing algorithm Collision occurs when hashing algorithm

produces same disk address for two different produces same disk address for two different keyskeys

ReturnReturn


Processing Stored DataProcessing Stored Data

Transactions processed to update a Transactions processed to update a master filemaster file Transactions - a business event such as a Transactions - a business event such as a

salesale Master file - data that is updated when a Master file - data that is updated when a

transaction occurs, such as a sales file or transaction occurs, such as a sales file or inventory fileinventory file

Two main methods of processing dataTwo main methods of processing data Batch processingBatch processing Transaction processingTransaction processing


Batch ProcessingBatch Processing

Transactions collected into Transactions collected into groups or batchesgroups or batches Batch processed and master Batch processed and master

file updated when the file updated when the computer has few users computer has few users onlineonline

Very efficient use of Very efficient use of computer resourcescomputer resourcesMaster file current only Master file current only immediately after immediately after processingprocessing

ReturnReturn


Transaction ProcessingTransaction Processing

Processing transactions as Processing transactions as they occurthey occur Also called real-time Also called real-time

processing and online processing and online processingprocessing

Terminals must be connected Terminals must be connected directly to the computerdirectly to the computer

Offers immediate updating Offers immediate updating of master fileof master file

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capron 8 ppt 06

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