System Use Sharing Protocol

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File Format
Name System Use Sharing Protocol
Released ~1991

System Use Sharing Protocol (SUSP) is a standard that specifies a uniform way to extend ISO 9660 (CD-ROM) format, to attach arbitrary metadata to each file. It is standardized as IEEE P1281.

Format details

Each ISO 9660 member file has an optional "system use area", whose use is undefined by the ISO 9660 standard. SUSP divides this area into tagged "entries", and defines some standard entry types. Other standards built on SUSP, notably Rock Ridge, define additional entry types.

Technically, non-core entries are namespaced, using the extension ID string in one or more "ER" entries. Known ID strings:

  • "RRIP 1991A" = Rock Ridge 1.09, 1.10
  • "IEEE_P1282" = Rock Ridge 1.12
  • "IEEE_1282" = Arguably a valid Rock Ridge ID
  • "AAIP_0100", "AAIP_0200" = AAIP

Some extensions (e.g. zisofs) that maybe ought to be SUSP lack their own "ER" ID, and instead are essentially rogue extensions of Rock Ridge.

Refer to ISO 9660#Extensions for a list of extensions, some of which are extensions of SUSP and/or Rock Ridge.

The Wikipedia article for Rock Ridge also has a list of entry tags.


The known versions of SUSP include the byte sequence 53 50 07 01 be ef. In most cases, this sequence will appear at offset 2048×{the 32-bit little-endian int at offset 32926} + 34.


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