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