High Sierra

Latest revision as of 18:27, 5 February 2026

High Sierra format (HSF) is a filesystem used on some early CD-ROMs. It is the predecessor of ISO 9660.

[edit] Nomenclature

There are two main, and mutually incompatible, formats in the High Sierra/ISO 9660 line of filesystems: the older format, which has a "CDROM" signature in the volume descriptors, and the newer format, which has a "CD001" signature.

It's tempting to assume that High Sierra refers to the older format, and ISO 9660 to the newer format. Unfortunately, while that is often the case (and is the convention used in this article), it is not always the case. Both names have been used to refer to the set of both formats.

[edit] Disambiguation

The filesystem format is not to be confused with macOS High Sierra, a version of the macOS operating system, also known as macOS v10.13 (Wikipedia article).

[edit] Identification

If a typical High Sierra filesystem is dumped to a raw image file in a typical way, the ASCII signature "CDROM" appears at offset 32777, and also 2048 bytes later at offset 34825.

[edit] Specifications

• Volume and File Structure of Compact Read Only Optical Discs for Information Interchange HTML Version
• Macintosh Technical Note #209: High Sierra & ISO 9660 CD ROM Formats

[edit] Sample files

• https://archive.org/details/shareware-grab-bag → Shareware Grab Bag.iso
• https://archive.org/details/MS_BOOKSHELF_87 → Microsoft Bookshelf circa 1987
• https://archive.org/details/cia-world-factbook-1989-cd-rom → CIA Factbook circa 1989

[edit] Links

• Wikipedia: ISO 9660 - Includes some historical information about High Sierra
• OS/2 Museum: Looking for High Sierra