[Beowulf] X5500 - ECC Registered or Unbuffered?

[Steffen Persvold]

Orion Poplawski wrote:
> Jan Heichler wrote:
>>
>> Don't forget DDR3-ECC memory which must be registered.
> 
> 
> http://www.siliconmechanics.com/i22789/2U-4-node-server.php shows 
> options for "ECC Unbuffered" or "ECC Registered".  No idea what the 
> practical difference would be.  Anyone?

Registered DIMMs = higher density (i.e larger in storage size), but 
typically with a latency penalty since there is a register on the dimm 
for Address/Control signals that delay them by 1 clock cycle. So your 
CL4 Ubuffered DIMM would become a CL5 Registered. In addition Registered 
DIMMs have a PLL on the module to "freshen" up the clock signal.

Unbuffered DIMMs cant have so high density (i.e many chips) on them 
because of load to the control/address signals (more load = lower signal 
quality).

Cheers,
--Steffen