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Floppy disk/drive curiousities

Posted: Wed Jun 10, 2020 10:43 am
by Ash
I am particularly curious about floppy disks and floppy drives and would really love it if I had some direction on what to search, where to read up on much of this, rather than just specific answers alone to my questions. Does the SPS actually retain documentation like this anywhere and would it be available for access?

I noticed that floppy drives support more than 80 tracks/cylinders and wanted to know, why is that a thing? 81, 82, 83, 84 tracks? Why would these be necessary? Are there documents describing this somewhere? Were there any systems that actively used these track layouts intentionally?

Double sided extended density floppy drives (2.88MB, pretty similar to standard HD disks, except they used 34868 BPI and 900 Oe?) seemed to have existed very briefly, did any non-PC systems make use of them? Are there any known published titles on this format? It's my understanding they were identified by a second box hole under the HD hole? Would a PC that supports floppy drives even support 2.88MB properly? I expect Windows to not know how to work with that.

There is also the triple floppy disk, which I was under the impression was a different floppy disk medium entirely, but KryoFlux says it supports GCR.. Is that the same as Apple GCR? The specifications look different to what a regular floppy disk/drive can do?

Edit: Fixed typos and grammar.

Re: Floppy disk/drive curiousities

Posted: Wed Jun 10, 2020 6:45 pm
by SomeGuy
Tracks beyond the last officially defined track, are a thing because the heads slide along rails, and there is no defined mechanism to tell the head where to stop. It just keeps going until it hits anything that makes it physically stop, and drive electronics don't try to prevent that. As such, different drives may stop the head at different places, but they usually leave some margin so it does accidentally not stop before the 40th or 80th track.

Add in to that, most floppy disks extended the magnetic coating out about that far, also as a margin. Then add in that some wise guys used those for copy protection, extra mastering information, or extra storage, and now there is a need to be able to read them in.

The later NeXT computer systems came with a 2.88mb drive, and some NeXT software was released in that format.

Yes, the Kryoflux can read and decode GCR encoding, that is used by Apple II, C64, Macintosh, and others. But not all PC floppy drives are 100% compatible with this, as some filtering electronics on many drives are only optimized for MFM.

Re: Floppy disk/drive curiousities

Posted: Wed Jun 10, 2020 7:57 pm
by brightcaster
The tripple floppies have a totally different approach with a complete different hardware! They don't use an index hole for example but an index track with a separate head giving exact sector positions, similiar to what was done with hard sectored disk decades before!

There are also other formats which are impossible to read in a standard floppy drive connected to kryoflux hardware, like the Iomega-Zip or the Apple Twiggy floppies with 62,5 tpi.

There are some good readings on the net: ... sk_formats ... 180801.pdf


Re: Floppy disk/drive curiousities

Posted: Sun Aug 09, 2020 4:12 pm
by Zakion
Thank you for sharing the links, this disk preservation website looks really interesting. I will read more there later today when I get back to my Berlin property here