Hardware Reference
In-Depth Information
Microsoft with DOS) to read all High Sierra format discs, opening the way for the mass production
and acceptance of CD-ROM software publishing. Adoption of this standard also enabled disc
publishers to provide cross-platform support for their software and easily manufacture discs for
DOS, UNIX, and other OS formats. Without this agreement, 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 Standardization (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 Sierra, 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 Attachment 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
The ISO 9660 standard enabled full cross-compatibility among different computer and operating
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 and refinements. It has three
levels of interchange that dictate the features that can be used to ensure compatibility with different
systems.
ISO 9660 Level 1 is the lowest common denominator of all CD file systems and is capable 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 directories. 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 and extension
can be up to 30 characters long (both added together, not including the . separator). Finally, Level 3
interchange rules are the same as Level 2 except that files don't have to be contiguous.
Note that Windows 95 and later versions enable you to use file and folder names up to 255 characters
long, which can include spaces as well as lowercase and many other characters not allowed in ISO
9660. To maintain backward compatibility with DOS, Windows 95 and later associate a short 8.3
format filename as an alias for each file that has a longer name. These alias short names are created
automatically by Windows and can be viewed in the Properties for each file or by using the DIR
 
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