How to read Osborne 1 Floppies?

Chuck Guzis cclist at
Thu May 27 15:47:09 CDT 2021

On 5/27/21 12:21 PM, Fred Cisin via cctalk wrote:

> In 1981, when the Osborne 1 came out, I got some sample disks from it.
> So, other than TRS80s, which I had, those were also the first samples
> that I worked with.  I manually, a sector at a time, copied some files
> from those Osborne 1 disks using Superzap on TRS80.  THAT was the
> preliminary success that convinced me that it could be done, and gave
> the the impetus and confidence to write XenoCopy, in the next few years,
> after the 5150 came out.  (5150 came out August 11, 1981, but it took me
> 5 months to get one)   BUT, the 5150 couldn't do FM Single Density, so
> the PC-DOS version of XenoCopy didn't get an Osborne format until the
> MFM Double Density upgrade for the Osborne 1 came out.

I'd been cutting floppy controller code since about 1975; the weirdness
of the IBM PC design really made for some head-scratching.

Sometime in the 5150/5160 days, I published instructions on how to
modify a PC floppy controller that used the 765 with a WD926 data
separator.  It was quite simple--for some unknown reason, both of the
clock rate select lines were hard-wired.   Getting FM support was mostly
a matter of lifting one of those lines and running a jumper to the
MFM/FM output on the 765.

But then IBM and clones did the same sort of thing with the parallel
port adapter.   Changing one to bidirectional (and curiously
PS/2-compatible) was mostly a matter of lifting the output enable line
on an IC and tying it an unused bit in the control port.

Sometimes I wonder if IBM did this sort of stuff intentionally.


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