ISO 9660 CD-ROMs and the Macintosh

Summary: Problems encountered when using such media to publish CD-ROMs aimed at a public comprising Macintosh users. How to avoid the pitfalls of file naming conventions (amongst others). How to produce hybrid CD-ROMs on a PC.


This page is about problems encountered when using CD-ROM conforming to the ISO 9660 standard to transfer data and other files between PC and Macintosh, and more generally when publishing CD-ROMs aimed at a public comprising an undetermined number of Macintosh users.
On the other hand, if you're more interested in using CD-ROMs to transfer data files in the other direction (from the Macintosh to the PC), please visit our other page on ISO 9660 CD-ROMs.

ISO - A Good Publishing Solution?

Since the ISO 9660 format is an universal format, not strictly bound to the MS-DOS/Windows platform and accepted under Unix and Linux, it could be thought as a good solution to transfer data between the PC and the Macintosh, and more generally to publish data. Most of the time, you can't know at publish time what computer configuration the potential users will have. Amongst those users, there is some percentage of Macintosh users.
If you chose not to ignore them (and it could be a big mistake, in particular in some sectors like graphics, DTP, imaging and the like), it would be good to take the time to think about all those aspects.
Sadly, as soon as you begin to scratch the surface, you understand that many problems exists, bound to the limited support of the ISO 9660 standard on the Macintosh. But you should know that there are solutions.
The first pitfall is the Joliet file naming convention (which allows to use up to 64 characters to name files). The second difficulty is bound to the identification of files on the Macintosh. The third problem comes with applications.
Last but nor the least, even if one could consider that it is a rather cosmetical matter, the autostart feature can only work on a Macintosh from a HFS (Macintosh) volume.

Joliet Filenames

The ISO 9660 standard, in its first redaction (what we nowadays call generally the level 1 of conformity), only allowed filenames according to the 8+3 scheme: names in uppercase, comprising only letters, numbers and the underscore). Some other limits applied, but we can ignore them here. Microsoft issued an extension to the ISO 9660 standard, named the Joliet extension.
This Joliet extension allows up to 64 characters to name files and folders. Those characters are stored in Unicode, that is a two-bytes character set usable for almost all characters used in the world.

Joliet Support on the Macintosh

As long as we had only 8+3 filenames on CD-ROMs, the Macintosh had it easy to support ISO 9660 CD-ROMs (see anyway the identification problem, below).
Thomas Tempelmann published a new Joliet Extension which alleviates some of those problems. This extension displays only 31 characters, but doesn't fall back to the 8+3 filenaming convention, and gives the rest of the filename under the 'Information' menu.
Even if you can recommend to your potential public to download this free extension, you can't consider that it will be available on all target computers.

Identifying the Content of Files

The second difficulty finds its roots in the methods used to identify the contents of files. The ISO 9660 standard uses the classical suffix (extension) method, where a character string, separated from the main part of the filename by a dot, represents the nature of the file ("doc" for a document, etc.).
The Macintosh file system, on the other hand, uses another scheme, based on the signature. The signature is very flexible because it can express the contents of the file (file type string) and the applications which created the file (creator string).
The 'File Exchange' extension (formerly 'PC Exchange') allows the user to set up a lookup table of extensions and signatures, and there are some utilities to alleviate the problem of opening files which were created with an application which is not installed on the target computer.
It is nevertheless very difficult to foresee what will really happen on the target computer. More, you should know that many Macintosh users are very happy to be able to ignore such technical aspects.
Which brings us to the subject of applications...

How About Programs?

Macintosh files are not monolithic, but may be composed of two segments, called forks, i.e. the data fork and the resource fork. Macintosh programs are stored in the resource fork, and it is not possible to launch an applications which would be stored in the data fork.
This means that you can't simply put on an ISO 9660 CD-ROM a Macintosh application that you downloaded from the Internet (for an example, an application to view the data files you produced and stored on this same CD-ROM).

A Solution: hybrid CD-ROMs

In front of those four problems, there is a solution: the hybrid CD-ROM. With a hybrid CD-ROM, the Macintosh user sees the HFS part, and the PC user the ISO part. Those two "parts" are only apparently separated, and we prefer using the "view" concept (an ISO view and a HFS view). Apart from the catalogs (ISO catalog and HFS catalog), all files are stored in a single and same place.
The files are therefore shared (better said, can be shared). A file can be visible in both views or in a single one. This can be of interest, for an example, when a file is specifically aimed at a part of the public.


In the same vein, even if the data files are identical, the names can be different in the HFS view and in the ISO view, each one following the specific rules of the file system.

File Signatures

Since both catalogs (ISO and HFS) are isolated, it is possible to put in the HFS catalog all information elements which are usually stored there in the case of a classical (HFS) magnetic volume. The main aspect of this information is the signature. Files seen in the HFS view can be identified exactly as on a classical magnetic volume.

Macintosh Applications

It becomes possible to put on the hybrid CD-ROM (in the HFS view, of course) applications or installation programs when you wish that the user launches them or installs them. See our more specific page on the Installation of Macintosh Applications.

The Solution: MacImage

In the past, only software packages like Toast allowed to produce such hybrid CD-ROMs, but on a Macintosh computer.
Now, with MacImage, it is possible to do it on a PC.
MacImage page shows more detailled information and comprises several links to illustrated and commented walkthroughs showing how to proceed.

Logiciels & Services Duhem
3, rue Pierre Haret - F-75009 Paris (France) - Tel. (+33) [0]149 700 455 - SIRET 381 149 996 00047 - EEC VAT FR32 381 149 996
email: sales (at) — web: