To: "Ralf Quint via Freedos-user" <freedos-user@lists.sourceforge.net>;
Cc: "tsie...@softcon.com" <tsie...@softcon.com>;
Subject: [Freedos-user] XMS on a 8086;
17:38, July 30, 2025, "tsiegel--- via Freedos-user" <freedos-user@lists.sourceforge.net>:
On 7/30/2025 6:41 AM, Ralf Quint via Freedos-user wrote:
Sorry to disappoint you, but you can't run a "80826 specific programs
on a V20".
Wrong.
I've done it, multiple times.
More than likely, those programs didn't use any of the extended mode
functionality available on a 286, but nonetheless, they ran, and I
continued to run them fairly regularly right up until I upgraded my machine.
The NEC V20 chip didn't have the whole 286 command set, but it
apparently had enough of it that *some* 286 specific programs would work.
Perhaps my usage was only an edge case, but saying you can't do
something I did regularly puts you in the same class as the college IT
tech person in charge of the library systems who insisted you couldn't
run a cd-rom on an XT.
I invited him to my house to see the (not one) but two cd-rom drives I
had running on my xt machine (yes, that same NEC V20 machine).
They worked just fine, and so did running those (probably) edge cases of
80286 programs also running on that machine.
Unfortunately, I no longer have that machine, or I'd load it up and take
screen shots for you, but there's nothing I can do about it at this point.
Regardless, I think this has strayed off topic far enough.
Believe what you like, I know what worked, but if it's any consolation,
I had folks on fidonet not believing me either when I told them I was
doing the whole 286 thing either, so depending on your point of view,
you're in good company, don't feel bad.At least that would be an exaggeration.
Basically, the V20/V30 are drop-in replacements for the 8088 and 8086
respectively. Due to internal differences in the microcode, they are
at the same clock speed allowing for a modest 5-10% performance increase.
NEC decided for some reason to include most of the 80186 instructions,
though IIRC, with some quirks. Those instructions are also more or
less the difference between an 8086 and a real mode 80286. Of course
the V20/V30 do not support any of the 286 protected/virtual memory
features.
And the V20/V30 have a few NEC specific instructions, plus the
possibility to switch into 8080 mode and thus run CP/M-80 2.x
Ralf
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