How can I decode files saved from a pre-OSX Macintosh?

Pre-OS X files consisted of two separate "forks" — a resource fork and a data fork.

Ideally, use a commensurately old Mac that could read those files to examine their structure. If you were to examine the file's resource fork you may be able to determine the program used to create them. Those resource fork files will have commonly understood names that corresponded to various resources shared within that program — dialogs, icons, menus, fonts, pictures. Resources unique to that program will have a unique name, and that name is likely to be useful to determine the programs used.

https://developer.apple.com/library/archive/documentation/mac/pdf/ResEditReference.pdf

https://developer.apple.com/library/archive/documentation/mac/pdf/MoreMacintoshToolbox.pdf

The data fork is most likely binary and unreadable without the program.

Until the late 1990s there were no Macintosh genealogy programs as such. Leister Productions produced the first one which was released in the mid 1990s. I have its original floppy disks but they are elsewhere. I can get them if needed.

If those files were not created by some genealogical research program such as Reunion those files were most likely produced by AppleWorks, or Microsoft Word, or perhaps FileMaker. Knowing that information would be a great help.

Old Toad wrote:

What are the extensions of the genealogy files on the CD?

Pre-OS X files did not use filename extensions.

First you need to figure out what kind of files they are. Can you mount the CD? If so, when you click on the application data and press command-I, does it tell you anything about the creator application?

If they are genealogical files then I used a great programme iFamily for Leopard in 2014 (and most probably much earlier if I was to check my old Mac PPCs). iFamily for Mac is still around (works on at least Sequoia) but latest advice at July 2025 is that the developer (Warwick Wilson, KS Wilson and Associates Pty Ltd)) is working on his new website. The latest version though can be downloaded elsewhere.

What are the extensions of the genealogy files on the CD?

If they are .ged, .ics or .txt you should be able to open them with one of these genealogy apps:

The .txt file can be opened by any text app like TextEdit but you may not be able to make heads or tails of the contents. It may take a genealogy app to be able to get the links involved.

John Galt wrote:

Pre-OS X files did not use filename extensions.

Thanks. I thought they were still visible in Get Info but, like with so many things, I misremembered.