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

Just to clarify:

The 8250/SFD-1001 uses a Matsushita JU-570 or JU-570-2 drive mech.  The
C900 uses a JA-560-012 drive mech and the serial number on mine is in the
100s.  I have never seen another drive in the wild.  Other than the C900
documentation, I have not been able to find any other info on these
drives.

Hope this helps.
Santo



On Thu, Jan 11, 2024 at 7:15 AM Francesco Messineo <
francesco.messineo_at_gmail.com> wrote:

> 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.
> >
>
>