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Mixing DIMMs in servers

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Mixing DIMMs in servers

Customer question for Tarek that he needed some assistance:




My customer was trying to mix DIMMs with different voltage, when he did this test the server started randomly.


He used the following parts :


HP 4GB (1 x 4GB) Single Rank x4 PC3L-10600R (DDR3-1333) Registered CAS-9 Low Voltage Memory Kit


HP 4GB (1 x 4GB) Single Rank x4 PC3-12800R (DDR3-1600) Registered CAS-11 Memory Kit



Is that configuration supported ?


If no, do we have any documentation ?


Thank you in advance for your help.




Reply from Eirik:




Seems supported. The 1.35v DIMMs will be operating at 1.5v. Do check the rules for your particular model of server.


E.g. the DL380pGen8 Quickspecs mention :


General Memory Population Rules and Guidelines:

  • White DIMM slots denote the first slot of a channel. For 1 DPC (DIMM per channel) populate white slots only.
  • Install DIMMs only if the corresponding processor is installed.
  • If only one processor is installed in a two processor system, only half of the DIMM slots are available.
  • To maximize performance, it is recommended to balance the total memory capacity between all installed processors and to load the channels similarly whenever possible.
  • Populate DIMMs from heaviest load (quad-rank) to lightest load (single-rank) within a channel. Heaviest load (DIMM with most ranks) within a channel goes furthest from the processor
  • RDIMMs operating at either 1.35V or 1.5V may be mixed in any order, but the system will power them at the higher voltage.
  • Do not mix RDIMMs, LRDIMMs, and UDIMMs.
  • LRDIMMs are supported up to 3 DIMMs per channel.
  • Using the HP RBSU, 1.35V DIMMs can be changed to operate at 1.5V.
  • DIMMs of different speeds may be mixed in any order; the server will select a common optimal speed.
  • The maximum memory speed is a function of the memory type, memory configuration, and processor model.
  • The maximum memory capacity is a function of the memory type and number of installed processors.
  • HP memory from previous generation servers is not qualified on the DL380p Gen8 Server. Certain HP SmartMemory features such as memory authentication and enhanced performance may not be supported.
  • To realize the performance memory capabilities listed in this document, HP SmartMemory is required. For additional information, please see the HP SmartMemory QuickSpecs at:

For memory population rules and additional memory guidelines, please see the DL380p Gen8 user guide at




Any other help?