Re: Software for MS-DOS 1.25

Den Sat, 7 Oct 2017 12:37:05 +0100 skrev smf <smf@null.net>:
> On 06/10/2017 16:35, Michał Pleban wrote:
> 
> > Theoretically you could port different versions of MS-DOS if you
> > wrote a new IO.SYS file for them to interface with the Commodore
> > hardware (and most likely the 6509 code for it), but I don't think
> > this is feasible.
> 
> If you reverse engineered the commodore msdos 1.25 then porting msdos
> 2 (https://github.com/BlastarIndia/msdos) should be possible.
> 
> The other alternative would be to write an IBM PC compatible bios, so 
> you could boot original msdos/ibm/dr versions.

That would be a far better alternative if someone really wants to put
an effort to this.

I'd recommend studying the MS-DOS related stuff at S100computers. They
have made homebrew modern cards with 8088, 8086, 80286, 80386 and 80486
and also a so called "MS-DOS support card", and they have all the
instructions you probably need to make a PC BIOS yourself.

> > The computer is NOT PC-compatible. That's the biggest problem with
> > using old MS-DOS software, which often assumes the computer is a PC.
> 
> It's mostly video output that is the problem, alot of old
> productivity software used ansi or bios to increase their potential
> market and it should be possible to get those to run. Most games are
> out though.
> 
> The biggest hurdle is that it's such a unique system that you're 
> essentially on your own, so it's a lot of work and the end result is 
> going to be pretty poor.

Once upon a time I owned a PC motherboard with a broken keyboard port.
Using DOS CTTY COM1: I were able to run the simple programs that
shipped with MS-DOS like EDLIN and similar, but almost all other
software wanted to use the real keyboard. As a rule of thumb all
software that uses a fullscreen display, especially with color, will
likely not work on a non-PC-compatible MS-DOS machine without
alterations. But my experience is from late 80's so maybe earlier
versions do work on any MS-DOS computer.

However most software works both on an PC/XT 8088 class machine and on
AT >=286 class machines and also on almost-PC-compatible machines like
Ericsson's fist so called PC compatible, all having different keyboard
hardware. That means that most software should probably work if you
write a BIOS that emulates the BIOS calls for handling the keyboard (as
opposed to using the MS-DOS calls to read the default input device
which CTTY can redirect).

Also if the CBM 8088 card can have ram at $B0000 or $B8000 then it
might be possible to write 8088/6509 code that just copies this to the
screen ram, thus emulating CGA or MDA text mode. That way I guess that
most text mode software would work right out of the box.


P.S. I've thinking, purely theoretical, how a CBM 8-bit and
PC-compatible computer could work, and my idea is that most of the
slower I/O stuff that seldom gets used directly by PC software could
perhaps be emulated by the 65** CPU. If we were to redesign a "C128+"
with 8088 instead of Z80 (or both) then it should have had a CGA
compatible (but enhanced) 80 character video output, with real memory
mapped screen and attribute memory. With a way to trap and delay 8088
access to certain memory and I/O areas and emulate those, and such
graphics, it could probably run all PC software without much of the
typical PC hardware.

I'm not familiar with the 8088 card for CBM II / PET 700 but if there
is any chance to add an ISA slot then a real PC display card would make
good PC compatibility far easier to achieve.

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