Cromemco 4FDC, How do you format a disk?

From: Richard Erlacher <>
Date: Tue Jul 27 17:00:32 1999

You'll need to spend a bit of time studying out how the controller you're
using handles the drive select or even a cable select if it has separate
selection on the 34 and 50-conductor cables, and whatever it does to
manipulate the clock extraction circuits to derive the appropriate clock for
whatever data rate you're wanting. BE CAREFUL! Some controllers switch the
clock frequency as they make whatever assumptions they may make about the
nature of what's on each cable. In order to drive 3.5" diskettes, you need
to fool the controller and software into believing it's talking to a drive
on the 50-pin cable. Though the 8" drives have only 77 tracks, they have
the 360 rpm spin rate and most other parameters in common with the little
teensy drives. If your controller switched the clock assuming its top data
rate will be 250 kbps, you may have problems.


-----Original Message-----
From: Chuck McManis <>
To: Discussion re-collecting of classic computers
Date: Tuesday, July 27, 1999 3:29 PM
Subject: RE: Cromemco 4FDC, How do you format a disk?

>At 04:38 PM 7/27/99 -0400, Allison wrote:
>>The 1771 is a single density only controller and not suitable for use with
>>3.5" disks. You want a board with a 765 (compupro) or 1793 CCS and a raft
>>of others.
>Which defines, for the most part, the difference between a 4FDC and a
>16FDC. The latter used the 1793 I believe. I've got a copy of the Western
>Digital databook that has these ICs in it if someone needs a copy.
>BTW, I wrote the formatter for CP/M on the 16FDC (in Turbo Pascal no less
>:-)) and it simply loaded up a buffer, then did a write track and stuffed
>the buffer with an OUTIR instruction. (the board did wait states so this
>worked.) The process involved creating a buffer and using special 8 bit
>codes for "sector gap" and "index mark" and "sync mark". I've long since
>given away that code but the person I gave it to is lurking on this list...
Received on Tue Jul 27 1999 - 17:00:32 BST

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