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Storage

Discuss the various typesof media storage.

Understand thecharacteristic of the hard

disk & floppy disk. Understand how the data is

stored, fragmentation &defragmentation.

Differentiate among CD-

ROM, CD-RW, DVDs

CHAPTER 6

Objectives:

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Storage holds data, instructions and information

for future use. Inside your computer there are two

types of data storage:

Permanent - stay in the system even when the

computer's power is turned off.

Temporary - when the system is turned off, data in

temporary storage disappear.

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What is storage?

     Storage medium is physical material used for storage

     Holds data, instructions, and information for future use

Also called secondary storage

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Storage capacity / size High capacity storage devices are required for many

sophisticated programs and large databases.

Speed People prefer whichever that is fast, but the problem is,

it will cost more. The fastest storage is RAM HardDisk CD USB Flash Drive, Floppy and MagneticTape. The speed is usually measured by access time.

Access time Refers to the average time needed to locate data on the

medium. Measured in ms for secondary storage, ns for RAM.

Cost The faster the storage device , the more expensive it is.

RAM Hard Disk, CD, USB Flash Drive, Floppy.

4.1Criteria f or  rating secondary storage

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4.2 Magnetic Disk Storage

Based on the technology of representing

data as magnetized spots on the disk.

With a magnetized spot 1 bit and without

such spot 0 bit.

To open a file means:

read data from the disk by converting

the magnetized data to electrical

impulses that are sent to the

processor. Saving means:

writing data to disk by sending

electrical impulses from the processor 

to be converted to magnetized spots

on the disk.

1 1 10 0

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4.2.1 Diskettes

A removable round, flat

piece of Mylar plastic that

stores data and programsas magnetized spots.

Sizes of diskettes

3 ½-inches

shutter 

shell

liner 

magneticcoating

flexible thin film

metal hub

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Disk drive - device that holds,

spins and reads data from and

writes data to a diskette.

A diskette is inserted into a

sl ot , called the drive gate or 

drive door .

4.2.1 Diskettes

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4.2.2 Hard DisksWhat is a hard disk?

High-capacity storage

Consists of several inflexible,circular platters that store

items electronically

Components enclosed in

airtight, sealed case for 

protection

hard disk mountedin system unit

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4.2.2 Hard Disks

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4.2.2 Hard Disks What is a head crash?

Occurs when read/write head touches platter surface

Spinning creates cushion of air that floats read/writehead above platter 

Clearance between head and platter isapproximately two-millionths of an inch

A smoke particle, dust particle, or human hair 

could render drive unusable

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What are tracks and sectors?

Track 

is narrow

recording band

that forms full

circle on disk 

Sector

stores up to

512 bytes

of data

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DOS

 keeps track of the various portions of a file with adevice called a File Allocation Table (FAT).

The FAT is a directory of sectors; it serves as a guide in

locating all the clusters in which portions of a file are

stored.

F ormatting ± prepare a track on floppy so that the operating

system can write information on it.

The most common reasons to format a hard disk are:

1) Due to virus that cannot be removed without destroying

the boot sector.2) Due to bad sectors.

3) You are changing from one operating system to another 

and wish to remove everything from the drive.

Write-protect features - protect a diskette from being written

to.

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Sectors and Clusters

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4.2.2.3 Fragmentation and Def ragmentation

Defragment your own pc:

Start > program files > accessories > system tools > disk defragmenter 

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4.3 Optical Disk Storage

Is a removable disk on which data is written and read

through the use of laser beams.

A high-power laser beam is used to represent data by

burning tiny pits into the surface of a hard-plastic disk. To read data, a low-powered laser light scans the disk

surface

Main types of optical storage are :CD-R, CD-RW and DVD.

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laser

diode

laser

diode

prism prism

light-sensingdiode

light-sensingdiode

0 1

lens lenspit land

disc label

Step 1.Laser diode

shines a light

 beam toward

disc.

Step 2.If light strikes

a pit, it scatters.If light strikes a

land, it is

reflected back 

toward diode.

Step 3.Reflected light is

deflected to a

light-sensing diode,

which sends digital

signals of 1 to

computer. Absence

of reflected light is

read as digital

signal of 0.

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4.3 Optical Disk Storage

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CD-R (compact disc - recordable) Permits writing on optical disk where CD-R drive, CD-R

disks and accompanying software are required. Once

written, data can't be modified

CD-RW (rewritable)

Erasable disc allows you write on it multiple times. Towrite on CD-RW, you must use CD-RW drive

DVD-ROM (Digital video disc-ROM)

Looks like an audio compact disk but can store 4.7 to 17

GB, allowing great data storage, studio-quality video

images, and theater-like surround sound.

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How is data stored

on an optical disc?

Typically storedin single track

Track divided

into evenly

sized sectors

that storeitems

single track

spirals to edge

of disc

disc sectors

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4.3 Optical Disk Storage

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4.4 Magnetic Tape StorageOne of the first storage used with mainframe

computer.

It's a thin plastic tape that has been coated with

substance that can be magnetizedMainly used for backup

not used for primary method of 

storage because it is a sequential-

access media (slow to access data)

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How is data stored on a tape?

Sequential access

Reads and writes data consecutively, like music

tape Random access

Used on hard disks, CDs, and DVDs ² which

can locate particular item immediately

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4.4 Magnetic Tape Storage

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     What is online storage?

Service on Web that provides

storage for minimal monthly

feeFiles can be accessed from

any computer with Web

access

Large files can be

downloaded instantaneouslyOthers can be authorized to

access your data

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4.5 Online Storage