[TriLUG] 32+ GB RAM PC advice

[Ed Hill]

On Sun, 2004-09-12 at 12:03, Carlos J. Cela wrote:

> here...I have noticed that you can configure 32GB RAM only if you have 4 
> processors installed in the machine....do you know if in a 32GB RAM/Quad 
> Opteron any of the 4 processors can access the full range of memory? I 
> mean, if my application is single-threaded, can I use the 32GB od RAM or 
> just to 1/4th of it? is all of the memory shared? if so, why the '4 
> processors installed' requirement?


Hi Carlos,

As Kevin pointed out, each Opteron CPU has its own directly-attached
memory.  And in both dual and quad configurations, all of the Opterons
can see all of the system RAM.  So while its technically a NUMA
(Non-Uniform Memory Access) architecture, it is for all practical
purposes an SMP system since the links between the CPUs are extremely
low latency.

The Altix systems are also NUMA and they scale to 512+ CPUs.  See the
description of the new Columbia system being built at NASA Ames:

  http://www.nas.nasa.gov/About/Media/Releases/07_27_04_innovative.html

for a truly large memory (1TB RAM/node with 20 nodes) configuration.

Ed

-- 
Edward H. Hill III, PhD
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