Not sure about the difference, but here are the Dell validated 4GB memory sticks and 5 digit part numbers =
9F035 4GB, 667MHz, ECC
MWP63 4GB, 667MHz, ECC
DR397 4GB, 667MHz, ECC
UW730 4GB, 533MHz, ECC
Quad Channel FBD-DDR2 (Fully Buffered DIMM) Memory support
ECC PC2-4200F 533 MHz or PC2-5300F 667 MHz FBD-DDR2 SD-RAM
256MB, 512MB, 1GB, 2GB, 4GB DIMM sizes
512MB minimum/32GB maximum
Thanks for that list with part numbers. I'm still confused though since most of the ram I look up on ebay with those part numbers still says for servers only. Is that just what this machine takes?
I found my answer. Most sellers list it only as server ram, but being that it is a workstation, and technically not a desktop, that's what kind it takes. I have found more that have correctly pointed this out.