SOP Benchmark: 286 Unix vs. 386 Unix

[Steve Benz]

>From article <2173 at sugar.UUCP>, by karl at sugar.UUCP (Karl Lehenbauer):
> It is somewhat surprising to me that the 386 would outperform the 286
> by a greater than 10-to-1 margin.  I would expect 3-to-1 from the clock
> and bus width differences.  I attribute the rest of the difference to
> the much nicer instruction set provided by the 386 in native mode
> (more registers and it's much more orthogonal) and the reduced overhead 
> of not having to manipulate segment registers.

  I'd say it has alot to do with 32-bit pointer manipulations.
It takes in many cases 6 instructions just to *copy* one pointer
to another -- I wouldn't even want to think about how many cycles
are involved in such an operation.  On the 386 it's two instructions
for (I think, but I could be wrong) all cases of 32bit-32bit moves.
(At least all the cases that pcc will generate.)

  You wouldn't do so well if you were comparing a 286 program in
small model to a 386 program.

> -- uunet!sugar!karl

				- Steve Benz