Find out how the CD can be used for
games, multimedia and computer data as well as music.
Since compact discs store audio in a digital format, they are
suitable for storing other information that can be represented in a
digital form. In 1984, Philips and Sony released the Compact Disc Read
Only Memory (CD-ROM) specification, known as the
Yellow Book. This
defines the necessary additions to the Red Book for the storage of
computer data. The CD-ROM disc is therefore like a pre-recorded floppy
disk with a very large capacity. Any computer data can be pre-recorded
on a CD-ROM.
The physical parameters of CD-ROMs are
identical to those defined in the Red Book. However CD-ROM discs differ from CD audio
discs in two important ways.
- The data on a CD-ROM disc are divided into sectors containing user data
error correction codes.
- The data are contained in files and so a file system is needed so that the required files can be
accessed easily and quickly.
The user normally will not need to be bothered with the
sector structure but will be aware of the file structure of files on a CD-ROM. There are now several formats based on the CD-ROM
specification covering a range of applications.
CD-ROM discs are read by CD-ROM drives, which have been standard
components of personal computers and some games consoles for a number of
years (DVD-ROM drives, which are now replacing CD-ROM drives will also
read CD-ROM discs). A CD-ROM has several advantages over other forms of
data storage, and a few disadvantages.
- Capacity of a CD-ROM is nearly 700 megabytes (MB) of data, the
equivalent of nearly 500 high-density floppy disks.
- The data on a CD-ROM can be accessed much faster than a tape, but
CD-ROMs are slower than hard discs.
- Like audio CDs you cannot write to a pre-recorded CD-ROM but only
to recordable versions.
The data on a CD-ROM can be accessed much faster than a tape,
particularly using the latest high-speed drives (52x is now common). To
reduce the maximum angular velocity these faster drives use CAV
(constant angular velocity) rather than CLV (constant linear velocity).
Therefore the data rate for data near the inside is less than the data
rate at the outside of the disc. For example a 40x drive gives a maximum
data rate of between 2.8 and 6 MB/s, depending where on the disc the
data is being read. Faster drives can create problems so some drives
make use of multiple laser beams to increase the data rate without
increasing the angular velocity.
|In this page:
- "Any computer data can be pre-recorded on a CD-ROM"