I have purchased a Dell T7500 workstation which has a single W5580 CPU and 6 DIMM slots available. I initially plan to run a 32-bit O/S on this particular PC but eventually will migrate it to a 64-bit O/S. My question concerns selecting the proper memory for it. Looking at the 5500 series memory rules it seems that if I were to populate all 6 DIMM slots the max memory speed will be reduced to 1066MHz (because there would be two DIMMs per channel). Thus to keep the option of running 1333MHz memory I would like to populate only 3 DIMM slots.
Since I initially am going to run a 32-bit O/S I only need to have about 4GB memory. So, between these configurations would I likely see any difference in system performance if I populate the DIMM slots like this (assume all DIMMs are 1333MHz):
1) A single 4GB RDIMM (utilizes 1 channel - allows for 2 additional 4GB DIMMS later for a 64 bit O/S)
2) Two 2GB RDIMMs (utilizes 2 channels - allows 1 additional DIMM for 64 bit O/S)
3) A 2GB RDIMM + two 1GB RDIMMS (utilizes 3 channels but would require replacing DIMMs to have more memory available)
Also, are there any advantages/drawbacks to using UDIMMs if I use only 3 DIMMS?
It gets down to tradeoffs between bandwidth, cost, and expandability.Option 2 might be the best thing for you at this point as it's higher bandwidth than option #1 and a "balanced" configuration (as opposed to option #3).We've been recommending a balanced configuration (same DIMM type, same population per channel) whenever possible, as configs such as your #3 may cause the effective bandwidth to drop down to option #2 levels (as measured by STREAM) due to how the memory controller works.
With regards to your UDIMM question, using UDIMMs with ECC will likely be a lower cost option for 1GB and 2GB DIMMs.You still get memory ECC, and you still can run with DDR3 1333 when populating 1 DIMM per channel - populating all 6 DIMMs (2 DIMMs per channel) will drop the memory down to 1066 MHz.Of course, you need to check with Dell on what they support and the costs.