Mode-Specific GuidelinesFour memory channels are allocated to each processor. The allowable configurations depend on the memory modeselected.NOTE: x4 and x8 DRAM based DIMMs can be mixed providing support for RAS features. However, all guidelines forspecific RAS features must be followed. x4 DRAM based DIMMs retain Single Device Data Correction (SDDC) inmemory optimized (independent channel) mode. x8 DRAM based DIMMs require Advanced ECC mode to gainSDDC.The following sections provide additional slot population guidelines for each mode.Advanced ECC (Lockstep)Advanced ECC mode extends SDDC from x4 DRAM based DIMMs to both x4 and x8 DRAMs. This protects against singleDRAM chip failures during normal operation.Memory installation guidelines:• Memory modules must be identical in size, speed, and technology.• DIMMs installed in memory sockets with white release tabs must be identical and similar rule applies forsockets with black and green release tabs. This ensures that identical DIMMs are installed in matched pairs -for example, A1 with A2, A3 with A4, A5 with A6, and so on.NOTE: Advanced ECC with Mirroring is not supported.Memory Optimized (Independent Channel) ModeThis mode supports SDDC only for memory modules that use x4 device width and does not impose any specific slotpopulation requirements.Memory SparingNOTE: To use memory sparing, this feature must be enabled in the System Setup.In this mode, one rank per channel is reserved as a spare. If persistent correctable errors are detected on a rank, thedata from this rank is copied to the spare rank and the failed rank is disabled.With memory sparing enabled, the system memory available to the operating system is reduced by one rank perchannel. For example, in a dual-processor configuration with sixteen 4 GB dual-rank DIMMs, the available systemmemory is: 3/4 (ranks/channel) × 16 (DIMMs) × 4 GB = 48 GB, and not 16 (DIMMs) × 4 GB = 64 GB.NOTE: Memory sparing does not offer protection against a multi-bit uncorrectable error.NOTE: Both Advanced ECC/Lockstep and Optimizer modes support Memory Sparing.Memory MirroringMemory Mirroring offers the strongest DIMM reliability mode compared to all other modes, providing improveduncorrectable multi-bit failure protection. In a mirrored configuration, the total available system memory is one half ofthe total installed physical memory. Half of the installed memory is used to mirror the active DIMMs. In the event of anuncorrectable error, the system will switch over to the mirrored copy. This ensures SDDC and multi-bit protection.Memory installation guidelines:• Memory modules must be identical in size, speed, and technology.• DIMMs installed in memory sockets with white release tabs must be identical and similar rule applies forsockets with black and green release tabs. This ensures that identical DIMMs are installed in matched pairs -for example, A1 with A2, A3 with A4, A5 with A6, and so on.46
