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.

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.
The server supports only industry-standard double-data-rate 4 (DDR4), 1600, 1866, or 2133 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 Lenovo 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 following rules apply to DDR4 RDIMM speed as it relates to the number of LRDIMMs in a channel:
- When you install 1 LRDIMM per channel, the memory runs at 2133MHz
- When you install 2 LRDIMMs per channel, the memory runs at 2133 MHz
- When you install 3 LRDIMMs per channel, the memory runs at 1600 MHz
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.
The server supports a maximum of 24 single-rank, dual-rank RDIMMs or 24 quad-rank LRIMMs.
It is recommended to install DIMMs with the same rank in each channel.

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
Number of DIMMs	DIMM type	DIMM size	Total memory
24	Single-rank RDIMMs	4 GB	96 GB
24	Dual-rank RDIMMs	8 GB	192 GB
24	Dual-rank RDIMMs	16 GB	384 GB
24	Quad-rank LRDIMMs	32 GB	768 GB
24	Quad-rank LRDIMMs	64 GB	1536 GB

The RDIMM options that are available for the server are 4 GB, 8 GB, and 16 GB. The server supports a minimum of 4 GB and a maximum of 384 GB of system memory using RDIMMs.
The LRDIMM option that is available for the server is 32 GB and 64 GB. The server supports a minimum of 32 GB and a maximum of 1536 GB of system memory using LRDIMMs.
Note
The amount of usable memory is reduced depending on the system configuration. A certain amount of memory must be reserved for system resources. To view the total amount of installed memory and the amount of configured memory, run the Setup utility. For additional information, see Configuring the server.
A minimum of one DIMM must be installed for each microprocessor. For example, you must install a minimum of two DIMMs if the server has two microprocessors installed. However, to improve system performance, install a minimum of four DIMMs for each microprocessor.
DIMMs in the server must be the same type (RDIMM or LRDIMM) to ensure that the server will operate correctly.

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.

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

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

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