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Lecture 9 Storage. www.shahidrasul.com. Storage. What is storage ?. Holds data, instructions, and information for future use. Storage medium is physical material used for storage. Also called secondary storage. Storage. Kilobyte (KB). 1 thousand. Megabyte (MB). 1 million. Gigabyte (GB).

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Lecture 9 storage

Lecture 9Storage



  • What isstorage?

  • Holds data, instructions, and information for future use

  • Storage mediumis physical material used for storage

  • Also called secondary storage


Kilobyte (KB)

1 thousand

Megabyte (MB)

1 million

Gigabyte (GB)

1 billion

Terabyte (TB)

1 trillion

Petabyte (PB)

1 quadrillion

Exabyte (EB)

1 quintillion

Zettabyte (ZB)

1 sextillion

Yottabyte (YB)

1 septillion

  • What iscapacity?

  • Number of bytes (characters) a storage medium can hold


Functions as source of input

Creates output

  • What is astorage device?

Hardware that records and retrieves items to and from storage media


Process of transferring items from storage media to memory


Process of transferring items from memory to storage media


Stores …

Primary Storage

Memory (most RAM)

Items waiting to be interpretedand executed by the processor

Secondary Storage

Hard Disk

Operating system, applicationsoftware, user data and information

Flash Memory Cards and USB Flash Drives

Digital pictures or files to be transported

CDs and DVDs

Software, backups, movies, music



Floppy Disk

Small files to be transported

  • What isaccess time?

  • Time it takes storage device to locate item on storage medium

  • Time required to deliver item from memory to processor



Magnetic disks
Magnetic Disks

Trackis narrow recording bandthat forms fullcircle on disk

Sectorstores up to512 bytesof data

  • What aretracks andsectors?

Formatting prepares disk for use and marks bad sectors as unusable

Magnetic disks1
Magnetic Disks

  • What is afloppy disk?


  • Portable, inexpensive storage medium (also called diskette)




Thin, circular, flexible film enclosedin 3.5” wide plastic shell

metal hub

flexible thin film


Magnetic disks2
Magnetic Disks

Capacity: 1.44 MB

Sides: 2

Tracks: 80

Sectors per track: 18

Bytes per sector: 512

Sectors per disk: 2880

  • How do you compute a disk’s storage capacity?

  • Multiply number of sides, number of tracks, number of sectors per track, and number of bytes per sector

    • For high-density disk: 2 sides  80 tracks  18 sectors per track  512 bytes per sector = 1,474,560 bytes

Characteristics of a3.5-inch High-DensityFloppy Disk


Magnetic disks3
Magnetic Disks

hard disk installedin system unit

  • What is ahard disk?

  • High-capacity storage

  • Consists of several inflexible, circular platters that store items electronically

  • Components enclosed in airtight, sealed case for protection


Magnetic disks4
Magnetic Disks

Sample Hard Disk Characteristics

Advertised capacity 120 GB

Platters 3

Read/write heads 6

Cylinders 16,383

Bytes per second 512

Sectors per track 63

Sectors per drive 234,441,648

Revolutions per minute 7,200

Transfer rate 133 MB per second

Access time 8.9 ms

  • What are characteristics of a hard disk?


Magnetic disks5
Magnetic Disks

  • How does a hard disk work?

Step 3.When software requests a disk access, read/write heads determine current or new location of data.

Step 2.Small motor spins platters while computer is running.

Step 4.Head actuator positions read/write head arms over correct location on platters to read or write data.

Step 1.Circuit board controls movement of head actuator and a small motor.


Magnetic disks6
Magnetic Disks


  • What is acylinder?


  • Vertical section of track through all platters


  • Single movement of read/write head arms accesses all plattersin cylinder





Magnetic disks7
Magnetic Disks

  • What is ahead crash?

  • Occurs when read/write head touches platter surface

  • Spinning creates cushion of air that floats read/write head above platter

  • Clearance between head and platter is approximately two-millionths of an inch

  • A smoke particle, dust particle, or human hair could render drive unusable


read/write head






Magnetic disks8
Magnetic Disks


disk cache

first requestfor data—to disk cache

second requestfor data—to hard disk

hard disk

  • What is adisk cache?

  • Portion of memory that processor uses to store frequently accessed items


Magnetic disks9
Magnetic Disks

  • What is aminiature hard disk?

  • Provide users with greater storage capacities than flash memory

  • Some have a form factor of less than 1 inch

  • Storage capacities range from 2 GB to 100 GB

Magnetic disks10
Magnetic Disks

  • What areexternal hard disksandremovable hard disks?

  • Used to back up or transfer files

Removable hard disk—hard diskthat you insert and removefrom hard disk drive

External hard disk—freestandinghard disk that connects to system unit


Magnetic disks11
Magnetic Disks

SATA (Serial Advanced Technology Attachment) controller uses serial signals to transfer data, instructions, and information

EIDE (EnhancedIntegratedDrive Electronics) controller supports four hard disks, provides connections for CD and DVD drives

Chip and circuits that control transfer of items from disk

SCSI(SmallComputerSystemInterface)controller supports up to fifteendevices including hard disks, CDand DVD drives, tape drives, printers,scanners, network cards

  • What is adisk controller?

Magnetic disks12
Magnetic Disks

  • What is online storage?

  • Service on Web that provides storage for minimal monthly fee

  • Files can be accessed from any computer with Web access

  • Large files can be downloaded instantaneously

  • Others can be authorized to access your data


Optical discs
Optical Discs


  • What areoptical discs?

Push the button toslide out the tray.

  • Flat, round, portable metal discs made of metal, plastic, and lacquer

  • Can be read only or read/write

Insert the disc,label side up.

  • Most PCs include an optical disc drive

Push the same buttonto close the tray.

p. 366 Fig. 7-19

Optical discs1
Optical Discs

disc label





Step 3.Reflected light is deflected to alight-sensing diode, which sends digital signals of 1 to computer. Absence of reflected light is read as digital signal of 0.









  • How does a laser read data on an optical disc?

Step 2.If light strikesa pit, it scatters. If light strikes a land, it is reflected back toward diode.

Step 1.Laser diode shines a light beam towarddisc.

Optical discs2
Optical Discs

  • How is data stored on an optical disc?

  • Typically stored in singletrack

  • Track divided into evenly sizedsectorsthat store items

single trackspirals to edgeof disc

disc sectors

Optical discs3
Optical Discs

  • How should you care for an optical disc?

Do not exposethe disc to excessiveheat or sunlight

Do store thedisc in a jewelbox whennot in use

Do noteat, smoke, ordrink neara disc

Do not stack discs

Do hold a discby its edges

Do not touchthe undersideof the disc

Optical discs4
Optical Discs

  • What is aCD-ROM?

  • Compactdiscread-onlymemory

  • Cannot erase or modify contents

  • Typically holds 650 MB to 1 GB

  • Commonly used to distribute multimedia and complex software

Optical discs5
Optical Discs

  • What is the data transfer rate of a CD-ROM drive?

Ranges from 48X to 75X or faster


75  150 KBps = 11,250 KBps or 12.25 MBps

75X is 150 KBps (KB per second)

48X: 48  150 KBps = 7,200 KBps or 7.2 MBps


Optical discs6
Optical Discs

Stores digital versions of roll of film

Film developers offer Picture CD service

Can be modified using photo editing software

  • What is aPicture CD?

Step 1.Drop off film to be developed. Mark the Picture CD box on the film-processing envelope.

Step 3.At home, print images from Picture CD on your ink-jet photo printer.

Step 2.When you pick up prints and negatives, a Picture CD contains digital images of each photograph.

At a store, print images to Picture CD at kiosk.

Optical discs7
Optical Discs

  • What areCD-Rs and CD-RWs?

Must haveCD recorderor CD-R drive

CD-R (compact disc-recordable)

—cdisc you can write on once

Cannot erasedisc’s contents

CD-RW (compact disc-rewritable)

—ceerasable disc you can write onmultiple times

Must haveCD-RW softwareandCD-RW drive

Optical discs8
Optical Discs

  • What is aDVD-ROM(digital versatile disc-ROM or digital video disc-ROM)?

  • High capacity disc capable of storing 4.7 GB to 17 GB

  • Must haveDVD-ROM driveor DVD player to read DVD-ROM

  • Stores databases, music, complex software, and movies


Optical discs9
Optical Discs

  • How does a DVD-ROM store data?

  • Two layers of pits are used, lower layer is semitransparent so laser can read through

  • Some are double-sided

  • Blu-Ray discs currently have a storage capacity of up to 27 GB

Lecture 9 storage

  • What istape?

  • Magnetically coated plastic ribboncapable of storing large amountsof data at low cost

  • Primarily used for backup


Lecture 9 storage

  • How is data stored on a tape?

  • Sequential access

  • Reads and writes data consecutively, like music tape

  • Unlike direct access — used on floppy disks, Zip disks, hard disks, CDs, and DVDs — which can locate particular item immediately


Pc cards
PC Cards

  • What is aPC Card?

  • Adds capabilities to computer

  • Credit-card-sized device commonlyused in notebook computers

Miniature mobile storage media
Miniature Mobile Storage Media

  • What isminiature mobile storage media?

  • Storage for small mobile devices

Miniature mobile storage media1
Miniature Mobile Storage Media


Smart Media

Secure Digital

xD Picture Card

Memory Stick

  • What are common types of flash memory cards?


Miniature mobile storage media2
Miniature Mobile Storage Media

  • How does one type of flash memory card work?

Miniature mobile storage media3
Miniature Mobile Storage Media

  • What is aUSB Flash Drive?

  • Plugs in a USB port on a computer or mobile device

  • Storage capacities up to 4 GB

  • May eventually make the floppy disk obsolete

Miniature mobile storage media4
Miniature Mobile Storage Media

  • What is asmart card?

  • Stores data on microprocessor embedded in small card

  • Input, process, output, and storage capabilities

Microfilm and microfiche
Microfilm and Microfiche

Microfilm — 100- to215-foot roll of film

Microfiche — small sheet of film, usually 4”  6”

  • What aremicrofilmandmicrofiche?

Store microscopic images of documents on roll or sheet of film

Images recorded using computer output microfilm recorder

Microfilm and microfiche1
Microfilm and Microfiche

  • How do life expectancies of various media compare?

  • Microfilm and microfiche have longest life of any storage media

Putting it all together
Putting It All Together


  • What are recommended storage devices for home users?

  • 80 GB hard disk

  • Online storage

  • CD or DVD drive

  • Card reader/writer

  • USB flash drive and/or 3.5-inch floppy disk drive


Putting it all together1
Putting It All Together

Small Office/Home Office (SOHO)

  • What are recommended storage devices for small office/home office (SOHO) users?

  • 750 MB Zip drive

  • 120 GB hard disk

  • Online storage

  • CD or DVD drive

  • External hard drive for backup

  • USB flash drive and/or 3.5-inch floppy disk drive


Putting it all together2
Putting It All Together


  • What are recommended storage devices for mobile users?

  • 80 GB hard disk

  • Online storage

  • CD or DVD drive

  • Card reader/writer

  • Portable hard disk for backup

  • USB flash drive, and/or 2 GB PC Card hard disk, and/or 3.5-inch floppy disk drive


Putting it all together3
Putting It All Together


  • What are recommended storage devices for power users?

  • CD or DVD drive

  • 300 GB hard disk

  • Online storage

  • Portable hard disk for backup

  • USB flash drive and/or 3.5-inch floppy disk drive


Putting it all together4
Putting It All Together

Large Business

  • What are recommended storage devices for large business users?

  • Desktop computer

    • 160 GB hard disk

    • CD or DVD drive

    • Smart card reader

    • Tape drive

    • USB flash drive and/or 3.5-inch floppy disk drive

  • Server or Mainframe

    • Network storage server

    • 40 TB hard disk system

    • CD-ROM or DVD-ROM server

    • Microfilm or microfiche


Summary of storage
Summary of Storage

Floppy disks

Recordable DVDs

Zip disks

Rewritable DVDs

Internal hard disks


Portable hard disks

PC Cards

Recordable CDs

Flash memory cards and USB flash drives

Rewritable CDs

Smart cards, microfilm, and microfiche


Lecture Complete