Re: [gentoo-user] hardware advice for dual-processor set-up on gentoo

[Denis <denis.che@gmail.com>]

Ok, I felt compelled to find more info on the issue that Bob raised
with the memory bandwidth limitation on the Opterons, and here is an
excerpt from an article on anandtech.com on this issue:

"The one limitation that both AMD and Intel have is bandwidth.  In
order to maintain compatibility with present day Socket-940 and
Socket-939 motherboards, AMD could not increase the pincount of their
dual core processors.  The benefit is that AMD's dual core CPUs will
work in almost all Socket-940 and Socket-939 motherboards (more on
this later), but the downside is that the memory bus remains unchanged
at 128-bits wide and supports a maximum memory speed of DDR400.  So,
while single core Athlon 64 and Opteron CPUs get a full 6.4GB/s of
memory bandwidth, today's dual core CPUs are given the same memory
bandwidth to share among two cores instead of one.

AMD's solution to the problem will come in the form of DDR2 and a new
socket down the road, but for now there's no getting around the memory
bandwidth limitations.  Intel is actually in a better position from a
memory bandwidth standpoint. At this point, their chipsets provide
more memory bandwidth than what a single core needs with their dual
channel DDR2-667 controller.  The problem is that the Intel dual core
CPUs still run on a 64-bit wide 800MHz FSB, which makes Intel's
problem more of a FSB bandwidth limitation than a memory bandwidth
limitation."

So basically...  I would pretty much be buying an already outdated
technology if I were to purchase a dual Xeon or a dual Opteron system
now?

I guess the other advantage is that a good dual Xeon system with 4GB
RAM will run me around $3000, whereas a dual Opteron (with dual core)
system with 4GB RAM will run me more like $4300.  If the Opterons are
currently at their memory bandwidth limit, I will have spent the $4300
for nothing, especially since I need the fastest memory integration I
can get for my codes.

Would I be better buying a dual Xeon system if I needed to buy right
now instead of waiting for the bandwidth issue to be resolved?

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