On 7/29/2025 8:26 AM, tsiegel--- via Freedos-user wrote:
And the fact that the V20/V30 chips understand (most of) the 80186
command set is because NEC decided to add those, just like the added
8080 emulation mode. Beside being a tad faster than the equivalent
Intel chip, there is no function difference between an V20/V30 and an
Intel 8088/8086.
Now that makes no sense.
Well...
How can there be no functional difference if they support an
additional command set?
I objected to your statement that there is a functional difference
between an 8086 and an 8088.
If you try to run a 286 specific program on an 8086, it won't work, if
you run it on a necv20, it does, how that translates into no
functional difference is beyond me, but whatever works for you.
Sorry to disappoint you, but you can't run a "80826 specific programs on
a V20". 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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