The Joliet specification utilizes the supplementary volume descriptor (SVD) feature of ISO 9660 to specify a set of files recorded within the Unicode character set.
The ISO 10646 character set specification may be identified by an ISO 2022 escape sequence. By recording this escape sequence in an ISO 9660 SVD, this technique for identifying the Unicode SVD is compliant with the ISO 9660 specification. It also retains interchange by not disrupting the files referenced through the primary volume descriptor (PVD).
All that remains is to resolve minor technical ambiguities within ISO 9660 which arise as the result of the use of wide characters.
Because the use of this particular escape sequence in an ISO 9660 SVD is unprecedented up to this time, several of the restrictions which are imposed by ISO 9660 may be relaxed without significantly disrupting information interchange between existing systems from a practical standpoint.
This design approach has several benefits. For instance, the use of the existing ISO 9660 standard allows for straightforward integration with existing extensions to ISO 9660. The designs for the System Use Sharing Protocol, Rock Ridge extensions for POSIX semantics, CD-XA System Use Area Semantics, Apple's Finder Flags and Resource Forks, all port in a straightforward manner to the Joliet specification.
Also, the use of a new SVD eliminates the danger of breaking software compatibility with existing ISO 9660 systems. Existing software will simply ignore the Unicode SVD, and will simply use the PVD instead. This compatibility "safety-valve" makes the goal of relaxing the file system's restrictions easier.
This document describes how a CD-ROM may be constructed so that names on the volume can be recorded in Unicode while remaining in compliance with ISO 9660. The particular ISO 10646 character sets used here are UCS-2 Level 1, UCS-2 Level 2, and UCS-2 Level 3.
The basic strategy of CD-ROM volume recognition is the Volume Recognition Sequence, which is a sequence of volume descriptors, recorded one per sector, starting at Sector 16 in the first track of the last session on the disc. A receiving system reads these sectors and chooses a particular volume descriptor from the sequence. This volume descriptor acts as a kind of anchor upon which the remainder of the volume is constructed.