Re: Reading 8x50-floppies with 1.2 MB-drive?

From: Hársfalvi Levente (
Date: 2001-11-27 12:38:54


(I sent this e-mail this morning but seems like it haven't made it to
the list due to a problem at

William Levak wrote:
> On Mon, 26 Nov 2001, [iso-8859-1] Hársfalvi Levente wrote:
> > 8x50 ---> IBM 1.2M: mechanically incompatible (100tpi vs. 96tpi), and
> > logically incompatible (GCR vs. MFM, like above). Even if the PC could
> > read the non-MFM data stream (like with the Catweasel), the misalignment
> > would be a hard problem to solve.
> 8x50 drives are quad density and IBM 1.2M drives are high density.  They
> are nominally the same data density, but the magnetic films are different.
> The heads require different magnetic field strengths to read and write.

AFAIK SD, DD and QD are about the same in their magnetic parameters.

1.2M drives are surely capable of switching between "low" and "high"
density operating mode (that's why they can still record 360K DD disks).
With pulling the 'LD line low, the floppy controller can tell the drive
to switch to "low density" mode. (I experimented with this setting and
found that it's even significant during reading a disk. By setting the
PC drive onto a halftrack of a Commodore disk, I got a lot more false
spikes on 'RD when the drive was set to HD mode ( when 'LD was not

So from this side, I guess there would be no problems with either
reading or writing a 8x50 or SFD1001 disk in a PC 1.2M drive ...if there
were no differences in the track alignment. But there are.

Best regards,


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