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Multiple formats on the same floppy disk?


Veteran Member
Jul 30, 2003
Västerås, Sweden
Does anyone have insight in if, which and how floppy disk formats could be partially shared on the same floppy disk?

When it comes to so-called flippies (single sided formats like Commodore, Atari, Apple, BBC Micro, very early IBM PC etc), it is rather trivial. Place the format that potentially needs the index hole on the top side, and format the bottom side with another format that doesn't.

However what I'm considering is to format only parts of a floppy disk with one format, then format other tracks with another format. It would require the respective computers/drives that are reading the disk to look at different physical locations.

I've seen some combined Apple/C64 or Atari/C64 releases, but those usually take the flippy approach. As for Commodore format, I think I know how to set up only a partial format. The 1541 and compatibles mainly needs track 18 (directory) in the right position, then I suppose one could stick with formatting tracks 19-35 in Commodore format and when saving files, use custom allocation of blocks. It would leave tracks 1-17 free for any other GCR or MFM format.

Some systems look for track 0 or 1 rather than the middle of the floppy disk. Which systems are that, and could those be set up to share the disk with another format?

I should probably research the topic, e.g. for formatting programs that already can limit themselves to formatting half the floppy disk but I'm open for advice.

In case anyone likes to ask the WHY? question, let's say it is an experiment to see if it can be done, plus that I have a batch of single sided floppy disks that I might like to use for a multi-format release. Certainly I could limit myself to a Commodore-only release, which would mean software for PET, VIC, C64, perhaps Plus/4 etc on the same disk without the need for a partitial format.