3. CD-ROM
CD-ROM stands for compact disk read-only memory.
It is an optical disc used to store digital data,orginally
developed for storing digital audio. The data stored on
CD-ROM can only be read. It can cannot be deleted
or changed. CD-ROM is a portable storage device.
The data can be transferred from one computer to
another easily by using CD-ROM.
4. CD Structure
It 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.
6. CD-ROM DRIVE
It is also called a CD-ROM player, a device that can
read information from a CD-ROM. CD-ROM players
can be either internal, in which case they fit in a bay,
or external, in which case they generally connect to
the computer's SCSI interface or parallel port.
7.
8. Reading data from CD-ROM
A 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.
9. Pits and lands
The 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’
10. Reading Speed
Reading speed is measured in kB/s
Reading 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.
11.
12. Writing Data On CD-ROM
A 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.
13. Tracks and Sectors
For 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.
Tracks
14. File System
The 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.
15.
16. Storage Capacity of CD-ROM
Storage 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.
17. Advantages of CD-ROM
It is the least expensive way to store
large amounts of data and information.
CD-ROM disks are durable and easy to
handle.
Information can be stored on CD-ROM
for many years.
18. Disadvantage Of CD-ROM
The data cannot be edited.
It retrieves data and information more slowly
than magnetic disks.
19. Summary
Compact 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.