Replacing 8" drive with 3.5" drive on CP/M systems

From: Bjørn Vermo <>
Date: Thu Feb 10 05:59:05 2005

On Sun, 06 Feb 2005 15:11:29 -0500, Herb Johnson <>

> Briefly, I posted that I doubt that
> a single density (FM) only system, such as the earliest CP/M systems,
> could read and write successfully AND reliably to HD diskettes. Also, I
> suggested the consequences of an old system owner who converted to this
> "standard" and then found that noone else could read his disks. In
> short, for the oldest of systems, there may be good reasons to continue
> to use old, but well-known, formats, drives and disk media. My Web site
> has pages of technical info and articles compiled from previous postings
> on these technical issues.

I had some experiences of this when early HD disks arrived. They could not
be reliably written on older drives because the write heads did not create
a sufficiently strong magnetic field. Reading was never aproblem.
Bulk erasing the HD disk, then formatting and writing was workable. While
the old drives were not able to erase something written by a HD drive,
they were able to write sufficiently strong bit patterns that they could
be read reliably. Actually, I think the flux in the read heads would be
just as strong as from an old diskette.

Different brands of diskettes will behave differently. I was doing my
tests back then with Rhone-Poulenc diskettes, which are probably not on
the market anywhere today. Modern diskettes also seem to be of lower
quality (and a lot cheaper) than in the eighties.

Received on Thu Feb 10 2005 - 05:59:05 GMT

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