Showing results for 
Search instead for 
Did you mean: 
New member
1 0 0 0
Message 1 of 2
Flag Post

32GB RDIMM's in Z640 Workstation

HP Recommended
Microsoft Windows 7 (64-bit)



We would like to upgrade our Z640 machine to 256 GB of RAM. Our machine has a pair of Xeon E5-2690 v3 CPUs, so we plan on purchasing eight 32 GB modules.

Reading the Quickspecs page 20, it says that only load reduced RAM modules (LRDIMMs) are supported for 32 GBs.

However, when I searched for compatible modules at some makers websites (e.g. Kingston), they showed both regular 32 GB DIMMs and the load reduced 32 GB DIMMs as being compatible with this workstation.

If possible, I would prefer purchasing the regular ones, because they are cheaper. However, I'm worried about compatibility as noted in the HP quickspecs.

So, could anyone provide me some information on the actual compatibility of regular 32 GB DIMMs?

Level 11
4,481 4,464 406 933
Message 2 of 2
Flag Post
HP Recommended

load reduced dimms should be used as per HP, if you try normal regestered dimms they may give random errors  or the system may not even boot due to the number of memory ranks in use


i recomend you read up on the diffrence between the two so you fully understand why LD dims are required when using 32GB dimms for proper operation on your system


but in a nut shell:


Memory buffers are used in LRDIMMs to reduce the electrical loads of the ranks to a single load. This allows up to eight ranks on a single DIMM module. Systems using LRDIMMs can be configured with the largest possible memory. The drawback is increased power usage and higher latencies versus lower capacity RDIMMs.


RDIMMs add a register, which buffers the address and command signals.The integrated memory controller in the CPU sees the register instead of addressing the memory chips directly. As a result, the number of ranks per channel is typically higher: the current Xeon E5 systems support up to eight ranks of RDIMMs. That is four dual ranked DIMMs per channel (but you only have three DIMM slots per channel) or two Quad Ranked DIMMs per channel. If you combine quad ranks with the largest memory chips, you get the largest DIMM capacities. For example, a quad rank DIMM with 4Gb chips is a 32GB DIMM (4 Gbit x 8 x 4 ranks). So in that case we can get up to 256GB: 4 channels x 2 DPC x 32GB


LRDIMMs can do even better. Load Reduced DIMMs replace the register with an Isolation Memory Buffer (iMB™ by Inphi) component. The iMB buffers the Command, Address, and data signals.The iMB isolates all electrical loading (including the data signals) of the memory chips on the (LR)DIMM from the host memory controller. Again, the host controllers sees only the iMB and not the individual memory chips. As a result you can fill all DIMM slots with quad ranked DIMMs. In reality this means that you get 50% to 100% more memory capacity.

0 Kudos
Warning Be alert for scammers posting fake support phone numbers and/or email addresses on the community. If you think you have received a fake HP Support message, please report it to us by clicking on "Flag Post".
† The opinions expressed above are the personal opinions of the authors, not of HP. By using this site, you accept the Terms of Use and Rules of Participation