Re: Found something interesting re MS-DOS

On Thu, Jan 4, 2018 at 6:51 AM, Michał Pleban <lists@michau.name> wrote:

> Hello!
>
> Mia Magnusson wrote:
>
> > It seems like with this it could be possible to make a special CBM-II
> > version of MS-DOS that is as compatible with PC as the stock MS-DOS 3.3
> > (except for defragmentation utilities and similar stuff) but with the
> > possibility to use more of the disks for DOS. Choose a combination of
> > tracks, sectors and sides that gives a total number of sectors that
> > line up good with the number of sectors that's on a CBM disk.
>
> I have been thinking about that and I suppose there are better ways to
> do that than modifying IO.SYS (for which we don't have a source code
> anyway):
>
> * MS-DOS allows writing installable device drivers - they are meant to
> be written to support non-standard devices (such as CD-ROM drives) and
> it's a perfect example of where it would be applicable.
>
> * It might not even be necessary to write a driver at all - the diskette
> boot sector contains a parameter block with the number of tracks,
> sectors and heads. Modifying this information might be sufficient to
> support the bigger 8250 diskette, but I haven't tried it yet.
>
> > Perhaps two different formats, one that uses all of the disk except two
> > sectors for BAM and directory (to make it possible to read the
> > directory in CBM mode and realize that it's a MS-DOS disk and not just
> > a disk containing garbage that can be overwritten). The other format
> > would leave just enough space for the CBM-II PC emulator software with
> > BAM and directory entries on the disk, and leave the rest for MS-DOS.
> > (Or maybe it's already good enough as it is?)
>
> I don't think it's worth it to support two different formats. The
> current implementation leaves tracks 37-39 for the emulation layer, it's
> a bit over 21 kB reserved space. I am not sure this extra 21 kB is worth
> the effort (also, BAM is four sectors, not one).
>
> You can see the current implementation in the source code:
>
> https://github.com/MichalPleban/cbm2-pc-emulator/
> blob/master/src/8088/include/ipc.asm
>
> The function "IPC_SectorCalc" is responsible from translating between PC
> and CBM disk geometry.
>
> Regards,
> Michau.
>
>        Message was sent through the cbm-hackers mailing list
>

I have the actual MS DOS 1.25 used by Commodore engineering, plus some
related documentation.  By far CBM was focused on CP/M 86, not DOS 1.25 in
their internal efforts to do something with their 8088 co-processor .
There were many versions of CP/M, and many programs written for or migrated
to  it.  Honestly I think we all should consider focusing on CP/M, from a
practical/efficiency standpoint, if we really want to do things with the
8088 coprocessor card.

If I have not done so already on my web site I can post all CP/M disks that
I have for everyone with an 8088 card to use.  Please advise.

Bill


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