Mixing DIMMs on HP z840

[hansdebree]

My Z840 has 4 LRDIMMs ,  can I expand with  RDIMMs??

[DGroves · Accepted solution]

no, HP explicitly states in their documentation that mixing "LR" dimms with non lrdimms is not acceptable this is stated in the z840 quickspecs, part of which is posted below (note the last line)

For details on the supported memory configurations on the HP Z840 Workstation, please refer to the System Technical Specifications - System Board section of this document.

DIMMs should be equally distributed across all four memory channels for optimal performance.

Each processor supports up to 4 channels of DDR4 memory. To realize full performance at least 1 DIMM must be inserted into each channel.

The CPUs determine the speed at which the memory is clocked. For example, if a 1600MHz capable CPU is used in the system, the maximum speed the memory will run at is 1600MHz regardless of the specified speed of the memory.

You cannot intermix LR DIMMs with Registered DIMMs. The system will not work.

[hansdebree]

Thanks for the clear answer!

Do you know if it is allowed to expand 4   16GB-modules (evenly distributed) with 1 or 2   8GB-modules(all LRDIMMs)?

[DGroves]

Read the HP docs on your model system and you will have your answer

https://support.hp.com/us-en/product/hp-z840-workstation/6978842/manuals

or the HP white paper on memory configurations

https://www.manualslib.com/manual/928210/Hp-Z840-Workstation.html?page=22