Re: Reading Commodore 900 disks in the 8250 (LP)

On Thu, Jan 11, 2024 at 1:04 PM Michal Pleban <lists_at_michau.name> wrote:
>
> Hello!
>
> Francesco Messineo wrote on 10.01.2024 16:45:
>
> > according to this page
> > https://www.zimmers.net/cbmpics/c900.html
> > The 900 has a 96 tpi floppy drive, the 8250 has (for sure) 100 tpi
> > drives.
>
> I am not entirely sure that this info is correct (see how it also says
> it's 1.2 MB whereas the disks have in fact 1.0 MB capacity). I do know
> that the disk drive interface is identical to the one used in the
> 8250LP. The C900 documentation states that MFM support is incomplete,
> and only GCR is used in the disk controller code, so they would not need
> to bother with 96 TPI MFM disks. The C900 mech is also outwardly
> identical to the one from the 8250LP except it has a grey faceplate, so
> I think there's good chance it is simply the same 100 TPI mech.
>

if it supports only GCR (I assume the same format as the 8250?) then
why you need
to bother with MFM ?
If you know the actual format used it's easy to tell what is the
mechanism they used, if it's 80 tracks per side, then it's 96 TPI, if
it's 77 tracks per side, then it's 100 TPI.
Frank
> Regards,
> Michau.
>