Since compact discs store audio
in a digital format they are suitable for storing other digital
information. In 1984, Phillips 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 physical parameters of CD-ROMs
are identical to those defined in the Red Book. The use of
the data it contains is different. While audio CDs can be
played at only one speed, CD-ROM drives exist with a range
of speed options from normal (1x) to four times normal speed
(4x) and, now, 52x. As the speed increases the access time
CD-ROM discs differ from CD
audio discs in two important ways.
The data on a CD-ROM disc are
divided into sectors which contain both user data and other
data for control and (additional) error protection. The data
on a CD-ROM are contained in files. All CD-ROMs therefore
need a file system to enable the computer to access the required
file 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 the files on a CD-ROM.
In order to use CD-ROMs you
need to buy a CD-ROM drive (sometimes called a CD reader)
and connect it to your computer. A CD-ROM has several advantages
over other forms of data storage, and a few disadvantages.
It can hold 650 megabytes (MB) of data, the equivalent of
nearly 500 high density floppy disks. The data on a CD-ROM
can be accessed much more quickly than data on a tape, but
CD-ROMs are considerably slower than
hard discs. Like audio CDs you cannot write to a CD-ROM (but
CD recordable discs do exist), so they are only used for pre-recorded
data. In addition CD-E (Compact Disc Erasable) is now being
introduced. Which will enable you to re-record data on the
The CD-ROM specification
is defined in the Yellow Book which is based on the CD audio
format but for computer data. The salient parameters are shown
data bit rate
||at normal speed
data per sector
||2048 bytes full error
||at normal speed
||1 or 2
||1 or 2
||only with Mode 2
You must use "Disk at Once
Mode" Do not attempt to send us masters using "Track
Incremental". Hewlitt Packard and Sony burners are notorious
for defaulting to this mode so be aware! Check with your operational
manuals for details.
of our CDROMs:
of user data in CD-ROM mode 1 (2048 bytes/record) OR
up to 78 minutes of digital audio
@44.1Khz OR a combination
of the above (enhanced CD).
Data stored on a CD-ROM disc
is divided into sectors which are equivalent to the audio
frames for a CD audio disc. At normal playback speed 75 sectors
are read every second. For double speed CD-ROM drives this
increases to 150 sectors per second and so on. Seek times,
while the disc rotates to the required starting position,
will also reduce as speeds increase.
Because CDs were designed primarily
for audio, their use for computer data requires the addition
of header data and error correction codes which are included
in every sector. There are two different types of sectors
defined in the CD-ROM specification, mode 1 and mode 2 (the
latter being used for CD-ROM XA discs).
Mode 1 Sectors
Mode 1 sectors are intended
for the storage of computer data. They comprise of:
Header which consists of Minutes,
Seconds, Sectors (frames) and Mode (= 1).
2048 bytes of user data. Error
detection and correction codes to give the CD- ROM data extra
protection. While CD audio players are able to conceal uncorrectable
errors which may result from a scratched disc, CD-ROM data
(especially application code) needs to be error free.
Mode 1 sectors are the simplest
type and are used for most CD-ROM based formats which follow
the Yellow Book.
The first CD-ROM discs contained
Mode 1 sectors designed for general computer storage on CD.
Although not specifically designed for multimedia there are
a number of important multimedia formats which use mode 1
CD-ROM as the basic method for storing data on CD.
|MPC 1 &
||Based on Mac
||Data on disc
||Not 100% ISO
||Audio and Data
do I make sure my CDROM is going to work?
It is vital that you test your
CDROM one off master on as many different machines as possible.
If you follow the formats listed in this section then you
should have success. While we at OmniDisc wish you the greatest
satisfaction with your order, we can not
be held responsible for discs that fail due to improper pre-mastering.
about errors and glitches?
OmniDisc digitally transfers
your master and does not normally test for errors. If an error
or glitch is found on your finished CDs we will reference
your original master. If it is the fault of our glass master
and not your master we will rerun your
order free of charge to you. CDs will not be replaced unless
returned COD to us. - No CDs may be returned without first
obtaining an RMA number.
about track "0" and special mastering needs?
There is a feature that can
be obtained on a CD-R master that utilizes track "0".
This can be used as a special data area or hidden area from
standard audio CD players. While this clever usage of the
CDROM is possible it does carry a premium price for glass
mastering. Please ask customer service about these charges
and any other nonstandard formats that you may require.