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CD-ROM
Formats
A number of CD-ROM formats have been defined to
suit different applications and needs |
The table below summarises the various CD-ROM based formats. Mode 1 formats
are based on the normal CD-ROM specification. Mode 2 are based on CD-ROM
XA.
The following diagram summarises the formats and shows the
relationships between them. Note that CD-i, Video CD and Photo CD
are all based on the CD-ROM XA and CD-i Bridge specifications and
comprise Mode 2 sectors. CD Extra discs also use Mode 2
sectors. Other CD-ROMs tend to use Mode 1 but there is no reason
why Mode 2 Form 1 cannot be used.
Windows
and Mac CD-ROM Formats
The most common CD-ROM format uses Mode 1 sectors and ISO 9660
file system for Windows PCs and other platforms. Windows is
also capable of reading Mode 2 CD-ROM XA
discs, but Mode 1 is suitable for virtually all purposes.
Mac CD-ROMs use Mode 1 and the HFS (Hierarchical File Structure)
instead of ISO 9660 and are less common.
Hybrid CD-ROMs contain both the ISO 9660 and HFS file systems so they
can be read by both platforms. Hybrid CD-ROMs will normally
contain two versions of executable files (Windows and Mac versions) but
it is possible for both platforms to use common data files such as
video, graphics and audio.
CD-ROM
XA
CD-ROM XA (for eXtended Architecture) discs contain Mode
2 sectors and were designed to allow audio and other data to be interleaved
and read simultaneously. This avoids the need to load images first and then play CD audio
tracks.
The CD-ROM XA specification also defines
certain image and audio formats to use:
- The graphics formats include 256 colour modes which are
compatible with PC formats and CD-i.
- The audio used is ADPCM
(Adaptive Delta Pulse Code Modulation) which is also defined for CD-i.
This CD-ROM XA format has not been successful in itself but
there are three important formats based on it: Photo CD,
Video CD and CD
EXTRA. CD-i also uses mode 2 sectors and shares some
commonality with CD-ROM XA for example both use ADPCM audio.
CD-I
Bridge
CD-I Bridge is a Philips/Sony specification, for discs intended to play on CD-i players and other platforms such as the PC. It
comprises:
- Disc format defining CD-I Bridge discs as conforming to the CD-ROM XA specification.
- Data retrieval structure as per ISO
9660.
- A CD-i application program, which is mandatory and stored in the CDI
directory.
- Audio data coding which includes ADPCM and
MPEG.
- Video data coding for compatibility with CD-i and CD-ROM XA.
- Multisession disc structure including sector addressing and
volume space.
- CD-i related data since all CD-i players must be able to
read CD-i Bridge data
Examples of CD-I Bridge formats are:
- CD-Interactive (CD-i), an almost obsolete format developed by Philips
for multimedia edutainment
- Photo CD for storing photo files on a CD in a range of resolutions
suitable for display and printing, now rarely used
- Video CD for up to 74 minutes of video using MPEG-1 plus menus and
playlists
- Super Video CD offering higher quality MPEG-2 video.
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