>On a related note, I've found that for LL testing, the speed of a
>Pentium MMX and a Pentium II is about the same adjusted for clock speed,
>but for factoring, the P-II seems to finish in about half the time.
Perhaps because the LL test is critical on the FPU speed, whereas the
factoring code is critical on the integer part of the CPU, in particular
the efficiency of the (I)MUL instruction.
On a Pentium P5 ("classic" and MMX), (I)MUL takes a minumum of 9 clocks,
whereas a Pentium P6 (PPro, PII, PIII, Celeron, Xeon) can execute (I)MUL
in 4 clocks.
The 486 takes 13 to 42 clocks to execute a 32 bit (I)MUL instruction.
Probably more typically 42 than 13.
This would appear to adequately explain the performance difference
between P5 and P6, and also give an explanation as to why the 486 is
apparently so much less efficient even after correction for clock
speed.
Regards
Brian Beesley
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