
Disc Formats

CD Related

CD

CD-ROM

CD-R

CD-RW

VCD

SVCD

Super Audio CD

DTS-CD

CD+G

CDV/CD-V/CD+V

MiniCD

HDCD

Dual Disc

China Video Disc

DVD Related

DVD

DVD-R

DVD+R

DVD-RW

DVD+RW

DVD-RAM

DVD+R DL

DVD-R DL/DVD-R9

DVD+RW DL

MiniDVD

DVD-Audio

BluRay Family

BluRay

BD-R/BD-RE

HDDVD Branch

HD-DVD

HD DVD-R

HD DVD-ROM

Other Formats

LaserDisc

Video Single Disc

MiniDisc

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CD-ROM (an abbreviation of
'Compact Disc Read-Only Memory') is a compact disc that
contains data accessible by a computer. While the compact disc format was
originally designed for music storage and playback, the format was later
adapted to hold any form of binary data. CD-ROMs are popularly used to
distribute computer software, including games and multimedia applications,
though any data can be stored (up to the capacity limit of a disc). Some
CDs hold both computer data and audio with the latter capable of being
played on a CD player, whilst data (such as software or digital video) is
only usable on a computer. These are called Enhanced
CDs.
Although many people use
lowercase letters in this acronym, proper presentation is in all capital
letters with a hyphen between CD and ROM.
CD-ROM discs are
identical in appearance to audio CDs, and data is stored and retrieved in
a very similar manner (only differing from audio CDs in the standards used
to store the data). Discs are made from a 1.2 mm thick disc of
polycarbonate plastic, with a thin layer of aluminium to make a reflective
surface. The most common size of CD-ROM disc is 120 mm in diameter, though
the smaller Mini CD standard with an 80 mm diameter, as well as numerous
non-standard sizes and shapes (e.g. business card-sized media) are also
available.
Data is stored on the disc as a
series of microscopic indentations ('pits', with the gaps between them
referred to as 'lands'). A laser is shone onto the reflective surface of
the disc to read the pattern of pits and lands. Because the depth of the
pits is approximately one-quarter to one-sixth of the wavelength of the
laser light used to read the disc, the reflected beam's phase is shifted
in relation to the incoming beam, causing destructive interference and
reducing the reflected beam's intensity. This pattern of changing
intensity of the reflected beam is converted into binary
data.
Standards
There are several formats used
for data stored on compact discs, known collectively as the Rainbow Books.
These include the original Red Book standards for CD audio, White Book and
Yellow Book CD-ROM[1]. ISO 9660 defines the standard file system of a
CD-ROM, although it is due to be replaced by ISO 13490. UDF format is used
on user-writable CD-R and CD-RW discs that are intended to be extended or
overwritten. The bootable CD specification, to make a CD emulate a hard
disk or floppy, is called El Torito. Apparently named this because its
design originated in an El Torito restaurant in Irvine,
California.
CD-ROM
format
A CD-ROM sector contains 2352
bytes, divided into 98 24-byte frames. The CD-ROM is, in essence, a data
disk, which cannot rely on error concealment, and therefore requires a
higher reliability of the retrieved data. In order to achieve improved
error correction and detection, a CD-ROM has a third layer of Reed-Solomon
error correction.[2] A Mode-1 CD-ROM, which has the full three layers of
error correction data, contains a net 2048 bytes of the available 2352 per
sector. In a Mode-2 CD-ROM, which is mostly used for video files, there
are 2336 user-available bytes per sector. The net byte rate of a Mode-1
CD-ROM is 44.1k×2048/(6×98) = 153.6 kB/s. The playing time is 74 minutes,
or 4440 seconds, so that the net capacity of a Mode-1 CD-ROM is 682
MB.
A 1x speed CD drive reads 75
consecutive sectors per second.
CD Sector
Contents
* A standard 74 min CD contains
333,000 sectors. * Each sector is 2352 bytes, and contains 2048 bytes
of PC (MODE1) Data, 2336 bytes of PSX/VCD (MODE2) Data, or 2352 bytes of
AUDIO. * The difference between sector size and data content are the
Headers info and the Error Correction Codes, that are big for Data (high
precision required), small for VCD (standard for video) and none for
audio. * If extracting the disc in RAW format (standard for creating
images) always extract 2352 bytes per sector, not 2048/2336/2352 bytes
depending on data type (basically, extracting the whole sector). This fact
has two main consequences: o Recording data CDs at very high speed
(40x) can be done without losing information. However, if done the same
with PlayStation or Audio CD it will result in an unreadable PlayStation
disc or an audio CD with lots of clicks because there are no error
correction codes and the errors are more likely to occur at high speed
recording. o On a 74 minute CD can fit very large RAW images, up to
333,000 × 2352 = 783,216,000 bytes (747 MiB). This should be the upper
limit for a RAW image created from a 74 min CD. If the stored standard
data (backup files), it can burn only 333,000 × 2048 = 681,984,000 bytes
(650 MiB). * Please note that an image size is always a multiple of
2352 bytes (the size of a block) when extracting in RAW
mode.
Manufacturing a
CD-ROM
Pre-pressed CD-ROMs are
mass-produced by a process of stamping, where a glass master disc is
created and used to make 'stampers', which in turn are used to manufacture
multiple copies of the final disc with the pits already present.
Recordable (CD-R) and rewritable (CD-RW) discs are manufactured by a
similar method, but the data is recorded on them by a laser changing the
properties of a dye or phase change material in a process that is often
referred to as 'burning'.
Capacity of a
CD-ROM
A standard 120 mm CD-ROM holds
650 or 700 MiB of data. To put this storage capacity into context, the
average novel contains 60,000 words. Assume that average word length is 10
letters and that each letter occupies one byte. A novel therefore might
occupy 600,000 bytes (600 kB, without layout information). One CD can
therefore contain over 1,000 novels. If each novel occupies at least one
centimetre of bookshelf space, then one CD can contain the equivalent of
over ten metres of bookshelf. However textual data can be compressed by
more than a factor of ten, using compression algorithms, so a CD-ROM can
accommodate at least 100 metres of bookshelf space.
In comparison a single layer DVD
contains 4.4 GiB of data, nearly 7 times the amount of a
CD-ROM.
Wikipedia information about
CD. This article is licensed under the GNU Free Documentation License . It uses material
from the Wikipedia article 'CD-ROM'
© Copyright disc-formats.guidechart.com 2008, All rights reserved.
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