Deciphering an odd floppy disk format.

Bob Smith bobsmithofd at
Tue Feb 16 13:07:11 CST 2021

I think by 75 we at DEC hwe had at least two pin compatible source for
UART,  While CHester G Bell gets credit for the design, my memory is
that Vince Bastiani did the design. That set the stage for having the
Synchronus /Isochronous chips built too. Signetics was contracted to
do the 2652 based on my lineunt design used in the DMC11 (similar to
DP8/e and DP11, but ssi chip count reduced and a good bit faster. The
SMC chip was based on Frank Zereksi's DU/DUP 11 design.

On Tue, Feb 16, 2021 at 1:04 PM Chuck Guzis via cctalk
<cctalk at> wrote:
> 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.
> --Chuck

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