1. Oracle Server X8-8 Service Manual
  2. Servicing Components
  3. Servicing CPU Module (CMOD) Components (FRU)
  4. Servicing DIMMs (CRU)
  5. DIMM Population Rules
  6. DIMM Rules

DIMM Rules

The DIMM installation rules aim to maximize the memory bandwidth available by spreading the memory across all six memory channels.

When installing DIMMs, consider the following rules:

  • When two DIMMs are in a channel, the channel speed defaults to the maximum supported speed (listed in the DIMM's SPD and read by BIOS) of the slowest DIMM in the channel. For example: if an 1866 MT/s-compliant DIMM is installed in a channel with a 2133 MT/s -compliant DIMM, the channel speed is limited to 1866 MT/s.

  • A maximum of 8 logical ranks (ranks seen by the host) per channel is allowed.

  • When one DIMM is used, it must be populated in DIMM slot 0 (farthest away from the CPU) of a given channel.

  • All CMODs should be populated identically.

  • Memory quantity needs to be equal across all CMODs.

  • All DIMMs in a system should be the same type and size.

  • Mixing of single-rank and dual-rank RDIMMs is not supported.

  • The minimum DIMM configuration as shipped from the factory is four 16-GB DIMMs in each CMOD, installed is slots D0, D6, D12 and D18.

    An upgrade of four DIMMs for each CMOD is allowed in this configuration by installing four DIMMs in slots D3, D9, D15 and D21.

  • Aside from an upgrade to the minimum shipped configuration (stated above), DIMMs must be added to each CMOD in sets of eight (one for each memory buffer channel). Add eight DIMMs to each CMOD starting with CMOD0 and ending with CMOD3 (four-CMOD configuration) or CMOD7 (eight-CMOD configuration). After all CMODs are populated, go back to CMOD0 and repeat the sequence adding the next set of eight DIMMs to each CMOD.

    For example: CMOD0 gets the initial eight DIMMs, followed by CMOD1 with the next eight DIMMs, continuing with all CMODs in the configuration. When 32 DIMMs (4-CMOD) or 64 DIMMs (8-CMOD) have been added across all CMODs in the configuration, go back to CMOD0 for the next set of eight DIMMs and continue this population pattern.

  • Each CMOD must only contain one size of DIMM. Mixing of different size memory within a CMOD is not allowed. Size mixing between CMODs is not allowed.

  • Mixing of LVDIMM and LRDIMM in the same chassis is not supported.