[ILUG] Advice much appreciated.

[Paul Jakma]

On Thu, 17 Feb 2005, Ronan Cunniffe wrote:

>   The only reason to use a 64-bit OS for number-crunching is if the 
> application specifically takes advantage of the 64-bitness.

You dont even need a 64bit chip for that. Most CPUs seem to have had 
SIMD extensions for a while, and most of them seem to include 64 bit 
data types. (RGBA @ 16bpc is 64 bit). MMX gives you 64 bit integer 
math (or 32bit * 2 at a time, or 16bit*4 or 8*8.)

> -------------------------------------
> I had someone with a problem with a 1.5MB working set.  We ran on a
> little laptop (P-M 1.4GHz, 2MB cache, 400MHz FSB) and a server CPU
> (Xeon 3.066GHz, 512MB cache, 533FSB).  Laptop won comfortably (~30 hours
> vs. ~35) despite being outclocked 2:1.

Pentium-M is quite a different design to the Xeon - you can't compare 
directly by clockspeed ;) (just as you can't compare Opteron to Xeon 
clock for clock, eg a 2.2GHz Opteron absolutely destroys a 2.4GHz 
Xeon in most of the ssl speed test, particularly the more complex 
ciphers.)

Also, I can't be bothered to find references, but ISTR that Intel's 
implementation of AMD64 somehow manages to not have any performance 
benefits over IA-32. Ie, if you could use the 64bit extensions, get 
the Opteron, not the Xeon.

> Ronan

regards,
-- 
Paul Jakma	paul at clubi.ie	paul at jakma.org	Key ID: 64A2FF6A
Fortune:
I cannot conceive that anybody will require multiplications at the rate
of 40,000 or even 4,000 per hour ...
 		-- F. H. Wales (1936)