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Dell PowerEdge R6525 Installation and Service Manual

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General memory module installation guidelines

To ensure optimal performance of your system, observe the following general guidelines when configuring your system memory. If your system's memory configurations fail to observe these guidelines, your system might not boot, stop responding during memory configuration, or operate with reduced memory. This section provides information on the memory population rules and about the non-uniform memory access (NUMA) for single or dual processor system.

The memory bus may operate at speeds of 4800 MT/s, 3200 MT/s, 2933 MT/s, or 2666 MT/s depending on the following factors:

  • System profile selected (for example, Performance Optimized, or Custom [can be run at high speed or lower])
  • Maximum supported DIMM speed of the processors
  • Maximum supported speed of the DIMMs
NOTE: MT/s indicates DIMM speed in MegaTransfers per second.

The system supports Flexible Memory Configuration, enabling the system to be configured and run in any valid chipset architectural configuration. The following are the recommended guidelines for installing memory modules:

  • All DIMMs must be DDR4 and above.
  • Mixing of memory module capacities in a system is not supported.
  • If memory modules with different speeds are installed, they operate at the speed of the slowest installed memory module(s).
  • Populate memory module sockets only if a processor is installed.
    • For single-processor systems, sockets A1 to A16 are available.
    • For dual-processor systems, sockets A1 to A16 and sockets B1 to B16 are available.
    • In Optimizer Mode, the DRAM controllers operate independently in the 64-bit mode and provide optimized memory performance.
      Table 1. Memory population rulesThe below tables describes the memory population information.
      Processor Configuration Memory population Memory population information
      Single processor Optimizer (Independent channel) population order A{1}, A{2}, A{3}, A{4}, A{5}, A{6}, A{7}, A{8}, A{9}, A{10}, A{11}, A{12}, A{13}, A{14}, A{15}, A{16} Odd amount of DIMMs per processor allowed.
      Dual processor (Start with processor1. Processor 1 and processor 2 population should match) Optimizer (Independent channel) population order A{1}, B{1}, A{2}, B{2}, A{3}, B{3}, A{4}, B{4}, A{5}, B{5}, A{6}, B{6}, A{7}, B{7} A{8}, B{8} Odd amount of DIMMs per processor is allowed. DIMMs must be populated identically per processor.
  • Populate all the sockets with white release tabs first, followed by the black release tabs.
  • In a dual-processor configuration, the memory configuration for each processor must be identical. For example, if you populate socket A1 for processor 1, then populate socket B1 for processor 2, and so on.
  • Unbalanced or odd memory configuration results in a performance loss and system may not identify the memory modules being installed, so always populate memory channels identically with equal DIMMs for best performance.
  • Minimum recommended configuration is to populate four equal memory modules per processor. AMD recommends limiting processors in that system to 32 cores or less.
  • Populate eight equal memory modules per processor (one DIMM per channel) at a time to maximize performance.
    NOTE:Equal memory modules refer to DIMMs with identical electrical specification and capacity that may be from different vendors.
Memory interleaving with Non-uniform memory access (NUMA)

Non-uniform memory access (NUMA) is a memory design used in multi-processing, where the memory access time depends on the memory location relative to the processor. In NUMA, a processor can access its own local memory faster than the non-local memory.

NUMA nodes per socket (NPS) is a new feature added that allows you to configure the memory NUMA domains per socket. The configuration can consist of one whole domain (NPS1), two domains (NPS2), or four domains (NPS4). In the case of a two-socket platform, an additional NPS profile is available to have whole system memory to be mapped as single NUMA domain (NPS0). For more information on the memory interleaving for NPSx, see the Memory interleaving population rules section in this topic.

BIOS implementation for NPSx
  • The BIOS Setup menu presents the applicable NPSx options based on the underlying model number. A change to the current NPSx is communicated to pre-BIOS firmware to take effect on the next boot. The default NPS setting is 1.
  • During boot, if the selected NPSx option is not allowed for the model number (for example, if the processor model number changes between reboot), system will halt at the end of POST with UEFI0388 message displayed. On the next reboot, the system will fall back to NPS1 default setting.
  • During boot, if the preferred interleaving for the current NPSx is not possible due to memory configuration (for example, the memory population is inconsistent with the preferred interleaving), BIOS shows a warning message UEFI0391.
    NOTE:System is functional when UEFI0391 message is displayed. However, the system may not be configured for optimal performance.
NPS system optimization

Optimal system configuration is dependent on the processor model, memory configuration, and NPS settings. Match the memory configuration with the NPS settings available for the processor.

Table 2. Supported NPS modes by ProcessorsThis table describes supported NPS modes by the processors.
Model Number NPS modes supported
7773X 4, 2, 1, 0
7573X 4, 2, 1, 0
75F3 4, 2, 1, 0
7713P 4, 2, 1
7663 4, 2, 1, 0
7513 4, 2, 1, 0
7543P 4, 2, 1
74F3 4, 2, 1, 0
7443 4, 2, 1, 0
7443P 4, 2, 1
7313P 4, 2, 1
7643 4, 2, 1, 0
72F3 4, 2, 1, 0
7742 4, 2, 1, 0
7702 4, 2, 1, 0
7662 4, 2, 1, 0
7642 4, 2, 1, 0
7552 2, 1, 0
7542 4, 2, 1, 0
7532 4, 2, 1, 0
7502 4, 2, 1, 0
7452 4, 2, 1, 0
7402 4, 2, 1, 0
7352 4, 2, 1, 0
7302 4, 2, 1, 0
7282 1, 0
7272 1, 0
7262 4, 2, 1, 0
7252 1, 0
7F72 2, 1, 0
7F52 4, 2, 1, 0
7F32 4, 2, 1, 0
7H12 4, 2, 1, 0
7713 4, 2, 1, 0
7543 4, 2, 1, 0
7763 4, 2, 1, 0
Table 3. Optimal NPS configurationThis tables describes the optimal NPS configuration.
Number of DIMMs per processor NPS
0 1 2 4
1 - - - X
2 - - - X
3 - - - X
4 - X - -
5 - - - X
6 - - - X
7 - - - X
8 X X - -
9 - - - X
10 - - - X
11 - - - X
12 - - X -
13 - - - X
14 - - - X
15 - - - X
16 X X - -
  • Recommended NPS setting is marked by X that indicate optimal performance.
  • NPS0 is only available for dual processor systems and is the preferred setting.
  • The NPS setting that are blank are functional. However, indicate non-optimal performance.
  • BIOS default NPS setting is 1.
  • UEFI0391 message may be displayed during boot if DIMMs are configured in the blank spaces of the table.
  • If the processor does not support the desired NPS setting for a given number of DIMMs, then use default setting (NPS1) and the UEFI0391 message is displayed.

Memory interleaving population rules

  • NPS4: Two channel interleaving
    • This interleaves channel [A and B], [C and D], etc.
    • Each channel within the pair requires at least one equal memory modules populated.
    • Works with three memory modules per channel pair, non-symmetrical module is stacked on top (odd configurations).
    • Any memory channel where one of the two channels is not populated is not interleaved.
    • There is no alternate, as all configurations can be mapped into this mode.
  • NPS2: Four channel interleaving
    • This interleaves the four channels on the left or right half of a processor which are channels [A, B, C, D] and [E, F, G, H].
    • All four channels require equal memory modules populated.
    • Each half or interleave set may have different total memory capacity with respect to each other.
  • NPS1: Eight channel interleaving
    • This interleaves all channels in a processor [A, B, C, D, E, F, G, H].
    • All channels in a processor require equal memory modules populated.
    • Single processor system creates a single NUMA node for the system.
      NOTE:An exception is allowed when system has 4-channels populated [C, D, G, H] with equal memory allowing the system to enter NPS1 mode even though all the 8 channels are not populated.
  • NPS0: Sixteen channel interleaving (dual processor)
    • This interleaves all 16 channels in a dual processor system.
    • All channels in a system require equal memory modules populated.
    • Dual processor systems create a single NUMA node for the system.

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