Deciphering an odd floppy disk format.

Chuck Guzis cclist at
Tue Feb 16 12:04:37 CST 2021

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

Even the bit ordering on some of the early controllers wasn't settled.
You can see LSB-first and MSB-first encoded floppies, GCR, MMFM, hard-
and soft-sector implementations.  There wasn't a strong push toward the
IBM implementations (3740/System 3) until the later part of the 70s.

All of which can make deciphering of the early floppy formats "interesting".

I was surprised in the mid-1970s on a remote console project that I
managed to find that the CDC engineers rolled their own UARTs from SSI.
 Apparently simpler to use off-the-shelf components for a couple-off
project than try to justify a part not in the parts crib already that
may or may not have a second source.


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