interesting Athlon/P4 discussion from FreeBSD-Q-l

Mark Hahn hahn at coffee.psychology.mcmaster.ca
Wed Apr 18 20:11:58 EDT 2001


> Cant vouch for correctness, but seems to have some explanations/info that
> werent mentioned here. Feel free to rebut the content of course.

the P4 has an awesome combination of hardware prefetcher,
fast FSB, and dram that keeps up with it.  for code that 
needs bandwidth, this is very attractive.  and it's dramatically
faster than anything else in the ia32 world: 1.6 GB/s versus
at most around .8 GB/s for even PC2100 DDR systems (at least 
so far - I'm hopeful that DDR can manage around 1.2 GB/s when
tuned, and if the next-gen Athlon contains hardware prefetch.)

but it's also true that most code, even a lot of computational code,
is not primarily dram-bandwidth-bound.  the P4 is not exceptional
when running real code in-cache; this is why on most benchmarks
other than Stream, recent Athlons beat P4's quite handily.

and that's why AMD is having such an awsome time in the market now,
and why Intel is cutting prices so dramatically on the P4.

regards, mark hahn.


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