[Beowulf] Opteron downrates DDR400 to DDR333 performance?

[V. B. Hunt]

Nate Faerber wrote:
> On Thu, 2006-02-02 at 14:05 -0600, NazarioJose at JohnDeere.com wrote:
>   
>> Hello, computer gurus -
>> do any of you know if the AMD Opteron downrates the PC3200 400 MHz DIMMS 
>> (DDR400) to 333 MHz (DDR333) performance  when the system has more that 2 
>> Gbytes of memory installed?
>>
>> i was told that when an opteron socke has more that 2GBytes of memory, then 
>> the cpu will automatically downrate the memory rate to an equivalence of 
>> DDR333 memory.
>>     
>
> It doesn't necessarily depend on the amount of memory installed.  It
> depends on the total number of ranks in your memory DIMMs which is
> likely determined by the number of DIMMs installed.  You get downclocked
> to PC2700 once you hit 8 ranks total on a memory controller (one per
> Opteron CPU.)  So you could get 4GB of RAM on a processor if you use
> single ranked DIMMs.
>
> See section 4.1.3.4 here:
> http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/26094.PDF
>
> Find previous coverage of this subject here:
> http://beowulf.org/archive/2005-July/013377.html
>
>   
That makes much more sense than the little "benchmarking" article I 
found.  If I had more time, I may have found the white paper from AMD, 
but had to cut my search short to go pick up my daughter from half-day 
kindergarten (that and I don't often build Opteron machines for my 
customers, as most of my customers need mostly individual desktop 
machines for light-weight home use).


Brice Hunt