[Beowulf] Opteron downrates DDR400 to DDR333 performance?

Bruce Allen ballen at gravity.phys.uwm.edu
Sun Feb 5 05:30:52 PST 2006

> perhaps this is TMI, but the answer depends on which cpu rev you're 
> using (and whether the bios optimizes the memory controller.) the AMD 
> bios-writers doc cited earlier shows that 4 dimms (2xdouble, 2xsingle) 
> can still be used at ddr400 on rev e.  no config uses >6 CS's at DDR400, 
> and some drop to DDR333 at <=5 CS's.


I have a related question.

I have a system using Opteron 175s (rev e CPUs).  There are four memory 
slots per CPU.  Two are populated with KINGSTON KVR400X72C3A/1G 
http://www.valueram.com/datasheets/KVR400X72C3A_1G.pdf The specs describe 
this as: 128M x 72-bit 1GB (1024MB) CL3 DDR400 SDRAM (Synchronous DRAM) 
ECC memory module. The components on this module include eighteen 64M x 
8-bit (16M x 8-bit x 4 Bank)  DDR400 SDRAM in TSOP packages. The 
electrical and mechanical specifications are 1GB 128 x 64-Bit DDR400 CL3 
184-Pin ECC DIMM.

I have two questions:

(1) In the future, if I want to install ADDITIONAL memory in the OTHER two 
slots, will it be possible for me to retain DDR400 speed?  If so, what 
constraints will there be on the additional memory?  For example, could I 
use the same type?

(2) In my current configuration, using just two of the DIMMs described 
above, should the BIOS ECC chip kill setting be 'enabled' or 'disabled'?


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