Re: Apple ][gs VGA Card

[dempson@actrix.gen.nz (David Empson)]

In article <35usrd$691@cville-srv.wam.umd.edu>,
The Doctor <iigs@wam.umd.edu> wrote:
> David Empson <dempson@actrix.gen.nz> wrote:
> >As far as I know, the only difference between the V20 and V30 is the
> >data bus size: the V20 is 8-bit (i.e. 80188 clone), the V30 is 16-bit
> >(i.e. 80186 clone).
>        ^^^^^

That was actually a slight exaggeration.  The V30 is an 8086 clone
with the instruction set of the 80186.

> On page 74-75 of the PCT manual (I have version 1.31 of the manual), it
> says the V30 is a 8086 compatible processor.  I understand that the 8086
> is a 8/16 bit chip.

No, the 8088 is the 8/16 bit chip (8 bit data bus).  The 8086 is the
same chip with a 16 bit data bus.

> Now, if the V30 is 80186 compatible, how compatible would it be to a
> 286?

Not at all.  The 80186 has some minor improvements - a few more
instructions were added (and possibly some addressing modes?  I don't
have the details handy).

The 80286 added protected mode, which is what is usually required by
software than needs a 286.

A small number of programs that say they need a 286 but run in real
mode actually only need the extra 186 instructions.  These programs
will run on a V30.  One example is the 4DOS command line program
(replacement for COMMAND.COM).  This can take advantage of the extra
instructions (but doesn't require them).

> I'm looking for a C++ compiler that works on the PCT, but shareware
> compilers are for 286 and higher (didn't try it since I thought it
> would be incompatible, also I think it requires more than 640k).  C++
> compilers for the 8088/8086 are pretty much obsolete.  Sorry for
> going off on this tangent. 

These definitely won't work.  One example that comes to mind is
Borland C++ 3.1, which we use at work.  This requires a 286 processor,
and it uses a DOS extender to provide access to extended memory.

> If those data books can answer how compatible the V30 is to the Intel
> equivalents, I would be much appreciated.

Basically, software compatible with the 186.
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand