Got 8' drive on PC working

[Vintage Computer Festival]

On Sat, 5 Mar 2005, Eric Smith wrote:

> Sellam wrote about 8-inch drives:
> > Aren't there supposed to be 26 sectors per track?
>
> That would be the standard format for DD (MFM) 256-byte sectors,
> or SD (FM) 128-byte sectors.  But if you set the PC BIOS to
> believe it is a 5.25" HD disk, it should think it's PC 1.2M format,
> 15 sectors of 512 bytes.  It will also think that there are 80
> tracks/side, while the drive only supports 77, so it's not surprising
> that there were problems on the last tracks.

Ok, makes sense.  So the new calculation is:

107520 / 512 = 210 / 15 = 14.  The second time I tried to format a disk
under DOS (to demonstrate to Mr. Johnny Lawson) I heard way more
recalibrations than I did the first time.  14 tracks worth sounds about
right.

> It never would have occurred to me that you'd try to use MS-DOS to
> format 8-inch disks. I thought you were just trying to read disks.

Well, I needed some way to test whether the setup was working.  It
basically is.  Now, on to reading those CP/M disks.

It was fun booting my PC into DOS 6.22 off an 8" drive though.

> Anyhow, older versions of MS-DOS allowed you to tell FORMAT
> how many tracks to use, though I'm not sure it was actually
> willing to accept arbitrary values.  And I'm not sure what
> DOS 6.22 allows.

I experimented very briefly with this the last time I tried getting this
to work but not enough to come up with anything conclusive.  DOS does seem
to expect a certain combination of "sane" values.

-- 

Sellam Ismail                                        Vintage Computer Festival
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