Memory module installation

The following notes describe the types of DIMMs that the server supports and other information that you must consider when you install DIMMs.

Confirm that the server supports the DIMM that you are installing (see the IBM ServerProven website).
When you install or remove DIMMs, the server configuration information changes. When you restart the server, the system displays a message that indicates that the memory configuration has changed. You can use the Setup utility to view the server configuration information, see Using the Setup utility for more information.
The server supports only industry-standard double-data-rate 4 (DDR4), 1600, 1866, 2133 or 2400 MHz, PC4-12800, PC4-14900, or PC4-17000 registered or load deduction, synchronous dynamic random-access memory (SDRAM) dual inline memory modules (DIMMs) with error correcting code (ECC). See the IBM ServerProven website for a list of supported memory modules for the server.
- The specifications of a DDR4 DIMM are on a label on the DIMM, in the following format.
  gggggeRxff PC4v-wwwwwm-aa-bb-ccd
  where:
  - ggggg is the total capacity of the DIMM (for example, 1GB, 2GB, or 4GB)
  - eR is the number of ranks
    1R = single-rank
    2R = dual-rank
    4R = quad-rank
  - xff is the device organization (bit width)
    x4 = x4 organization (4 DQ lines per SDRAM)
    x8 = x8 organization
    x16 = x16 organization
  - v is the SDRAM and support component supply voltage (VDD)
    Blank = 1.2 V specified
  - wwwww is the DIMM bandwidth, in MBps
    12800 = 12.80 GBps (DDR4-1600 SDRAMs, 8-byte primary data bus)
    14900 = 14.93 GBps (DDR4-1866 SDRAMs, 8-byte primary data bus)
    17000 = 17.00 GBps (DDR4-2133 SDRAMs, 8-byte primary data bus)
  - m is the DIMM type
    L = Load Reduction DIMM (LRDIMM)
    R = Registered DIMM (RDIMM)
  - aa is the CAS latency, in clocks at maximum operating frequency
  - bb is the JEDEC SPD Revision Encoding and Additions level
  - cc is the reference design file for the design of the DIMM
  - d is the revision number of the reference design of the DIMM
Note
To determine the type of a DIMM, see the label on the DIMM. The information on the label is in the format xxxxx nRxxx PC4v-xxxxxx-xx-xx-xxx. The numeral in the sixth numerical position indicates whether the DIMM is single-rank (n=1), dual-rank (n=2), or quad-rank (n=4).
The following rules apply to DDR4 RDIMM speed as it relates to the number of RDIMMs in a channel:
- When you install 1 RDIMM per channel, the memory runs at 2133 MHz
- When you install 2 RDIMMs per channel, the memory runs at 1866 MHz
- When you install 3 RDIMMs per channel, the memory runs at 1600 MHz
- All channels in a server run at the fastest common frequency
- Do not install registered and load reduction DIMMs in the same server
The maximum memory speed is determined by the combination of the microprocessor, DIMM speed, DIMM type, Operating Modes in UEFI settings, and the number of DIMMs installed in each channel.
In two-DIMM-per-channel configuration, the compute node automatically operates with a maximum memory speed of up to 1600 MHz when the following condition is met:
- Two 1.35 V single-rank, dual-ranl, or quad-rank RDIMMs or LRDIMMs are installed in the same channel. In the Setup utility, Memory speed is set to Max performance and LV-DIMM power is set to Enhance performance mode. The 1.35 V UDIMMs, RDIMMs or LRDIMMs will function at 1.5 V.
The compute node supports a maximum of 16 single-rank, dual--rank RDIMMs or 16 quad-rank LRIMMs.

The following table shows an example of the maximum amount of memory that you can install using ranked DIMMs:

Table 1. Maximum memory installation using ranked DIMMs.
Four column table documenting the total memory with different configurations.
Number of DIMMs	DIMM type	DIMM size	Total memory
16	Single-rank RDIMM	4 GB	64 GB
16	Single-rank RDIMM	8 GB	128 GB
16	Dual-rank RDIMM	8 GB	128 GB
16	Dual-rank RDIMM	16 GB	256 GB
16	Quad-rank LRDIMM	32 GB	512 GB

The RDIMM options that are available for the compute node are 4 GB, 8 GB, and 16 GB. The compute node supports a minimum of 4 GB per CPU and a maximum of 256 GB of system memory using RDIMMs.
The LRDIMM option that is available for the server is 32 GB. The compute node supports a minimum of 32 GB per CPU and a maximum of 512 GB of system memory using LRDIMMs
A minimum of one DIMM must be installed for each microprocessor. For example, you must install a minimum of two DIMMs if the compute node has two microprocessors installed. However, to improve system performance, install a minimum of four DIMMs for each microprocessor.
DIMMs in the compute node must be the same type to ensure that the compute node will operate correctly.
The memory rank sparing mode requires an even number of DIMMs. If your server has an odd number of DIMMs installed, ensure that you disable the memory rank sparing mode from the Memory menu in Setup Utility. See Using the Setup utility for more information.
Note
After disabling the memory rank sparing mode, if a message prompts that the memory configuration is not valid, restart the integrated management module 2.1 (IMM2.1). Alternatively, you can turn off the server, disconnect it from and then reconnect it to ac power, and then turn on the server again.
When you install one quad-rank DIMM in a channel, install it in the DIMM connector furthest away from the microprocessor.

Note

You can install DIMMs for microprocessor 2 as soon as you install microprocessor 2; you do not have to wait until all of the DIMM slots for microprocessor 1 are filled.
DIMM slots 9-16 are reserved for microprocessor 2; thus, DIMM slots 9-16 are enabled when microprocessor 2 is installed.

The following illustration shows the location of the DIMM connectors on the system board.

Figure 1. The location of the DIMM connectors on the system board

The following memory-channel configuration table shows the relationship between the processors, memory channels, and the DIMM connectors.

Table 2. Memory-channel configuration table
Channels	Processor 1 – DIMM connectors	Processor 2 – DIMM connectors
Channel 0	7 and 8	9 and 10
Channel 1	5 and 6	11 and 12
Channel 2	1 and 2	15 and 16
Channel 3	3 and 4	13 and 14

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