Re: [Fwd: Re: random variate from power exponential distribution: continue]

[Linas Vepstas <linas at austin dot ibm dot com>]

On Tue, Oct 19, 2004 at 01:42:27PM +0200, Olaf Lenz was heard to remark:
> 
> What strikes me as most remarkable is that the AMD CPU actually seems to
> be ~30% faster than the Intel CPU, even though the Athlon has a lower
> clock rate! 

This is not supposed to be surprising: this is, after all, 
what cpu design is all about.   Different processors have a different
number of fixed-point and floating point units, interconnected in
various ways.  (This is called "super-scalar design") More exectution 
units usually means more work can be done per clock cycle.  Also, 
the goal of instruction dispatch is to keep each unit busy: better 
dispatching designs mean processors that can do more even if the 
clock speed is identical, and the number of execution units in
the chip are identical.

Note also, there are usually trade-offs.  One design might run
on type of algorithm very efficiently, and all other algos very 
poorly.   Your code may have an algo that the AMD athalon is
particularly good at;  other algos may run faster on intel,
or on power.  Don't make buying decisions on clock speed alone.
SPECmarks are much better indicator.

(Showing my age: In the very early days, circa power-1 (1988), 
the power-1 ran 4-8x faster than a 486, even though the 486 clock 
speed was 2 or 3x the power-1.  This is because the power-1 had
lots of execution units, and a much much better dispatcher. 
And more registers.  And more chip-memory bandwidth. And ...).

--linas