Re: Win32 and Win64

From: Mat Ballard (mat_at_chemwares.com)
Date: 03/07/05 

Date: Mon, 07 Mar 2005 10:09:11 +1100

Rudy Velthuis [TeamB] wrote:

> I think this may be an interesting read for the Win32/Win64 native
> supporters. I found some of the facts mentioned quite surprising.
>
> http://blogs.borland.com/abauer/archive/2005/03/03/2841.aspx

in which "As for the 64bit stuff, the Intel folks actually said that they have
seen many cases where 64bit applications were actually slower than their 32bit
counterparts!" - the implication being that there is little benefit in migrating
to 64 bit.

Jason Southwell hinted at the answer: independent benchmarking is now emerging
which confirms this - for INTEL chips. eg, the 32- and 64-bit POVRAY results in:

http://www.linuxhardware.org/article.pl?sid=05/02/24/1747228&mode=nocomment

where the P4s are about 10% slower in 64-bit than 32-bit where the Athlon 64s
are about 20% faster. this behaviour has been noticed in a number of
applications: eg http://www.lostcircuits.com/cpu/p4-600-64/6.shtml shows
virtually no benefit for Intel chips, but a 30% improvement for AMD chips.

Intel's chips are heavily dependent on a large cache to offset the effects of
branch mis-prediction in their long pipeline. crudely speaking, a 64-bit app
occupies twice as much cache as as 32-bit one, so depending on the application,
Intel's P4 may suffer badly from the 32->64 bit transition. AMD chips have a
shorter pipeline, are so are less dependent on cache.

so, if Intel's chip were the only game in town, the case for 64-bit is rather
weak (comes down to very large memory space), but with AMD chips you can get a
30-50% performance jump in some applications. that's worth it for just about any
server-based process.

cheers,

Mat

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