Deciphering an odd floppy disk format.

Mattis Lind mattislind at
Tue Feb 16 13:38:35 CST 2021

Den tis 16 feb. 2021 kl 19:04 skrev Chuck Guzis via cctalk <
cctalk at>:

> Building floppy controllers from MSI TTL was not uncommon, even after
> the debut of the WDC LSI chips, which were initially very expensive.

I got information from a person that worked for Q1 reseller in Denmark that
the floppy controller was built entirely out of TTL chips. No CPU
whatsoever. It was interfaced through a parallel bus to the main computer.

What is interesting is that it had variable record length. It was specified
during the format process which tracks had what number of records and their
size. The first track always had 40 bytes record since it was the INDEX
track. File allocation was on a track basis. In the INDEX file each file
then had a start track and stop track as well as information on how many
records there were in the file and what size each record was. Also the
number of records per track were included in the file specification.

I have never ever heard of such a scheme before.


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