AT&T 3B2 floppy format

Seth Morabito lists at
Sat Apr 2 15:44:40 CDT 2016

* On Fri, Apr 01, 2016 at 11:41:01PM -0700, Curious Marc <curiousmarc3 at> wrote:

> It looks like you did everything right. However I thought one
> specifies interleave directly in the BIN2IMD command using the DM=3
> option. I see you have DM=4 on your command line. But since you can
> load the kernel that might not be the source of your problem. Having
> a disk being formatted in one drive not readable in another could
> simply be that one of the two drives is misaligned. Or some silly
> difference with the track width between the two heads of your later
> HD drive and the earlier QD drive, although since they are both 80
> tracks that should not be. BTW, can you do the reverse, format a
> disk in your AT&T and recover every sector through IMD on your PC?
> In this case there might be an option in ImageDisk to write without
> formatting. I think you can do that with Omnidisk.  
> Marc

Hi Marc,

DM=3 in the BIN2IMD arguments list has nothing to do with
interleaving. It specifies Data Mode 3, 300kbps MFM.  But it turns
out, this WAS my problem!

After doing more experimentation this morning, I've discovered that
the data mode I should have been using was 250kbps MFM, NOT 300kbps!

After changing ImageDisk to write 250kbps (and ensuring that the
300RPM "I" jumper was strapped on the FD55-GV), the images work

So, that's the secret. 3B2 floppies are DSQD 250kbps MFM.



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