3.5" floppy drive question(s)

Fred Cisin cisin at xenosoft.com
Sat Oct 11 19:04:48 CDT 2008

On Sat, 11 Oct 2008, Chuck Guzis wrote:
> We were plagued by customers simply changing diskettes whenever they
> felt like it.  Relying on a checksum-after-select scheme such as that
> used by CP/M and early MS-DOS versions was pretty ugly (and not at
> all airtight, something that plagued MICROSO~1 no end).

Why didn't MICROS~1 ever document that the CPM ^C was fully enabled to
flush the disk buggers?

> playing with the driver, I noted that the write protect signal was
> conditioned only on select, not on motor, head-load or ready.
> Experimenting with some of the other engineers to see how fast one
> could insert and remove a floppy gave a safe polling interval of
> about 250 msec, which was barely noticeable in normal system
> operation and performed only if there were open files on the drive.
> Some of the single-sided 600 RPM Sony (0A1?) drives were also used in
> a few CP/M systems, such as the Preis.  It was a very noticeable
> improvement over 5.25" media.
> Cheers,
> Chuck

Fred Cisin                      cisin at xenosoft.com
XenoSoft                        http://www.xenosoft.com
PO Box 1236                     (510) 558-9366
Berkeley, CA 94701-1236

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