Some time ago, I thought it would be useful to understand exactly what is the difference between CD-ROMs recorded in the old High Sierra format versus the ISO 9660 standard. This was in part spurred by the fact that I have a number of CD-ROMs/images that use the High Sierra format (Microsoft Programmer’s Library, some IBM Developer Connection issues, OS/2 Warp 4, and more) that both macOS and Windows 10 refuse to mount. The other part of my motivation was the usual insatiable curiosity.
Finding the actual text of the High Sierra Working Paper (also High Sierra Proposal, i.e. proposed standard) turned out to be rather unexpectedly difficult. I found a number of articles talking about the High Sierra Proposal (HSP) but not the actual HSP text.
The closest thing I could find was an article in the excellent PC Tech Journal in the July 1987 issue (Patterning CD-ROM by Peter Jansson, page 163). Said article recaps the HSP in very good detail but it’s not the actual text. But even that was enough to show that although the structure defined in the High Sierra format is not far from the ISO 9660 standard, the two data structures are just different enough to be mutually incompatible.
Even though the High Sierra Proposal is long obsolete, and it never even was an official standard, it was the de facto standard from mid-1986 until ISO 9660 was approved. In addition, it wasn’t about until July 1988 that MSCDEX 2.0 with ISO 9660 support started shipping, which means that until then CD-ROMs in ISO 9660 format would have been unusable in practice.
It was even worse than that. MSCDEX shipped with CD-ROM drives, and existing CD-ROM drive owners had MSCDEX 1.x which only supported the High Sierra format (HSF). MSCDEX 2.0 was not a free upgrade, which is why until about 1990, CD-ROMs in ISO 9660 format were exceedingly rare.
The same problem was presumably present on the mastering side: Existing CD-ROM publishers had software which supported only the High Sierra format and since it worked just fine, they weren’t motivated to spend money (probably quite a lot of it) on upgrades. Since ISO 9660 isn’t really any more capable than the original HSF, publishers had very little incentive to use ISO 9660 and a lot of good reasons to stick with HSF.
As a case in point, Microsoft’s C 6.0 (May 1990) or Programmer’s Library 1.4 (June 1991) CD-ROMs used the High Sierra format, not ISO 9660. That in turn meant that CD-ROM file system implementors were forced to support HSF for many years to come, otherwise users would rightfully complain that CD-ROMs that can be read just fine in DOS aren’t recognized. Sometimes CD-ROM publishers used HSF well into the 1990s for no apparent reason (e.g. IBM Warp 4 CD-ROM from 1996), but no one really noticed because everything worked just fine.
The High Sierra Working Paper (the actual title of the proposal) used to be available from NISO (National Information Standards Organization) in the late 1980s, but once ISO 9660 was approved, official standards bodies had no reason to distribute the obsolete proposal.
The full text of the HSP was almost certainly published in the 1986 book CD-ROM Standards: The Book by Julie Schwerin, ISBN 0904933547. The book is long out of print and not available used. I would love to get a copy (it should contain several related articles) but I just can’t find any.
Okay, so there’s no way to get the HSP through the front door. But maybe an alternate route might work? Surely someone must still have the full text.
My research showed that the original HSP editor was Howard Kaikow, which is why he was able to offer copies years later. I contacted his sister Rita but she was unfortunately not able to help me (not for lack of trying).
The next name on my list was Bill Zoellick, former manager of software research at TMS, Inc. and not coincidentally, co-author of a 1987 book titled File Structures: A Conceptual Toolkit. In 1986-1987, he published several articles dealing with the technical details of the High Sierra Proposal. Tracking him down was not entirely easy but after piecing together the evidence from several sources, I concluded that the Bill Zoellick who now teaches marine biology really is the same Bill Zoellick who was involved in the High Sierra Group 35 years ago. I e-mailed him and not much later, I had a freshly scanned copy of the High Sierra Working Paper in my inbox.
The High Sierra Working Paper
I ran the scan through OCR, which as a side effect did a good job of straightening the text (the text of the original was impressively askew on many pages). The document is now available here, and as far as I know, not available anywhere else.
After actually looking over the HSP, it became clear that it really was a draft of ISO 9660. The two texts are rather similar, with many sentences and paragraphs entirely identical, and many others with just minor editorial differences. The true technical differences between the HSP and ISO 9660 are not many, but one is that the descriptor signature changed from ‘CDROM’ to ‘CD001’ and the general descriptor layout changed just enough that everything is at a different offset.
The upshot is that even though software supporting HSP can be easily adapted to support ISO 9660 and vice versa, since the overall structure is quite similar, it does require a couple of small but key changes. That’s exactly why software which only supports ISO 9660 (like the CD-ROM image mounting software in Windows or macOS) has no chance of reading High Sierra images (it is difficult to call them ISOs).
More or less for the heck of it, but also in order to get a plain-text-ish version of the document for easier comparisons and for easy navigation within the document, I also produced a HTML version of the High Sierra Working Paper. It looks somewhat like the original, but it’s deliberately not using any CSS, which means that it can be almost perfectly displayed by antique browsers, like this Netscape Communicator 4.61 in OS/2 Warp 4 Convenience Pack 2.
I’ve not been able to find how the original High Sierra Working Paper was produced, i.e. what word processing/document processing software was used. I am fairly certain that the serif font used for the body of the text is Palatino… which only narrows it down to “printed on a PostScript printer”, i.e. not much at all. I have no idea what kind of software would have been used at Digital Equipment Corporation (where Howard Kaikow worked at the time) for this purpose back in 1986.
I’m now working on a longer article which will deal with the history of the High Sierra Group, examine the rationale behind the HSP, and attempt to track how the High Sierra Working Paper morphed into ISO 9660 via ECMA-119. That will still take some work and it’ll be published when it’s ready.