Hardware Reference
In-Depth Information
ment, the maturation of the optical marketplace would have taken years longer and the
production of optical-based information would have been stifled.
The High Sierra format was submitted to the International Organization for Standardiz-
ation (ISO). Two years later (in 1988), with several enhancements and changes, it was
republished as the ISO 9660 standard. ISO 9660 was not exactly the same as High Si-
erra, but all drivers that would read High Sierra-formatted discs were quickly updated to
handle both ISO 9660 and the original High Sierra format on which it was based.
For example, Microsoft wrote the MSCDEX.EXE (Microsoft CD-ROM extensions)
driver in 1988 and licensed it to optical hardware and software vendors to include with
their products. It wasn't until 1993 when MS-DOS 6.0 was released that MSCDEX
was included with DOS as a standard feature. MSCDEX enables DOS to read ISO
9660-formatted (and High Sierra-formatted) discs. This driver works with the AT At-
tachment Packet Interface (ATAPI) or Advanced SCSI Programming Interface (ASPI)
hardware-level device driver that comes with the drive. Microsoft built ISO 9660 and
Joliet file system support directly into Windows 95 and later, with no additional drivers
necessary.
ISO 9660
TheISO9660standardenabledfullcross-compatibilityamongdifferentcomputerandop-
erating systems. ISO 9660 was released in 1988 and was based on the work done by the
High Sierra group. Although based on High Sierra, ISO 9660 does have some differences
andrefinements.Ithasthreelevelsofinterchangethatdictatethefeaturesthatcanbeused
to ensure compatibility with different systems.
ISO9660Level1isthelowestcommondenominatorofallCDfilesystemsandiscapable
of being read by almost every computer platform, including UNIX and Macintosh. The
downside of this file system is that it is very limited with respect to filenames and direct-
ories. Level 1 interchange restrictions include the following:
• Only uppercase characters A-Z, numbers 0-9, and the underscore (_) are allowed in
filenames.
• Only 8.3 characters maximum for the name.extension (based on DOS limits).
• Directory names are eight characters maximum (no extension allowed).
• Directories are limited to eight levels deep.
• Files must be contiguous.
Level 2 interchange rules have the same limitations as Level 1, except that the filename
andextensioncanbeupto30characterslong(bothaddedtogether,notincludingthe.sep-
