By

Sadaf KhanJavaria KhalidSumayyah Ifra

CD-ROM

IndexStorage devices.Categories of storage devices.CD-ROM.

Structure of CD-ROM.Reading of CD-ROM.

Pits & Lands. Reading Speed.

Writing of CD-ROM. File System. Tracks & Sectors. Writing Methods.

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Storage Capacity.Advantage of CD-ROMDisadvantages of CD-ROM

Summary.References.Question & Answer Session

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The storage devices store data –even when the computer is turned off.

It is used to keep important data and files which are of regular use on permanent basis.

Storage Devices

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The two main categories are magnetic storage and optical storage.

Categories of Storage Devices

Optical StorageMagnetic Storage 06

CD-ROM stands for compact disc read-only memory. It is an optical disc used to store digital data, originally developed for storing digital audio.

CD-ROM

CD StructureA CD is flat, round, portable metal disc,

which is coated with a thin metal or plastic or other material that is highly reflective.

It is usually 0.75 inches in diameter and less than one-twentieth of an inch thick.

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Reading Data On CD-Rom

Reading data from CD-ROMA CD-ROM drive reads digital data from a

spinning disc by focusing a laser on the disc’s surface.

Some areas of the disc reflect the laser light into a sensor, and other areas scatter the light.

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Pits and landsThe CD-ROM holds digital data.Data is stored in the form of lands and pits.Lands are flat areas on the metal surface.Pits are depressions or hollows.

Reading logic ‘1’Reading logic ‘0’ 11

Reading SpeedReading speed is measured in kB/sReading speed determines the transfer of

data in one second.1× or 1-speed which gives a data transfer

rate of 150 kB/s in the most common data format.

Maximum speed available today is 52x.

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Writing Data On CD-Rom

Writing Data On CD-ROMA laser is used to heat a chemical dye in the

disc to create marks that will be read as data.

As marks (pits) are created through burns, this process is also referred as burning.

Burning a CD is comparatively slower than reading it.

Maximum burning speed is 32x.

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File SystemThe format of the CD (file system) describes

how the data is stored on the CD.The earliest file system was High Sierra

Standard.The ISO 9660 format is now the most

common format.

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Tracks and SectorsFor burning, the first process is to format a

blank CD.CD-ROM drive creates a set of concentric

rings, called tracks on each side of CD.Tracks are divided into short segments called

sectors.Sectors are where data is stored physically.

Tracks16

Writing MethodsThere are many methods to write a CD.Monosession: Creates a single session on

the disc.

Multisession: This method lets a CD to be written several times, by creating a 14MB-long table of contents (TOC) de 14Mo for each session.

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Storage Capacity Of CD-Rom

Storage Capacity of CD-ROMStorage capacity is the maximum limit of

data storage on a CD.A standard compact disc can store 650 MB of

data or about 70 minutes of audio.A new generation of compact disc, however,

can hold 700 MB of data or 80 minutes of audio.

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Advantages of CD-ROMLarge storage space

Compact and light

Can be manufactured on a large scale

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Disadvantage Of CD-ROMSlow Writing speed

Not easily re-writable

Cost Concerns

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SummaryCompact Disk is a type of optical storage.It holds data through physical marks.Its is played in a CD-Player, and is read at

different speeds.Files system is required to write data on CD

by different methods.CDs are compact storage devices that can be

moved from on place to another easily.There is always a doubt in their durability.

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Referenceswww.ecarta.comwww.howstuffworks.comwww.kioskea.comwww.youtube.comwww.wikipedia.orgwww.answers.com

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