84 Installing System ComponentsMode-Specific GuidelinesThree memory channels are allocated to each processor. The number ofchannels used and the allowable configurations depend on the memory modeselected.Advanced ECC (Lockstep) Mode SupportIn this configuration, the two channels closest to the processor are combinedto form one 128-bit channel. This mode supports Single Device DataCorrection (SDDC) for both x4- and x8-based memory modules. Memorymodules must be identical in size, speed, and technology incorresponding slots.Memory Mirroring SupportThe system supports memory mirroring if identical memory modules areinstalled in the two channels closest to the processor (memory should not beinstalled in the farthest channel). Mirroring must be enabled in the SystemSetup program. In a mirrored configuration, the total available systemmemory is one-half of the total installed physical memory.Optimizer (Independent Channel) ModeIn this mode, all three channels are populated with identical memorymodules. This mode permits a larger total memory capacity but does notsupport SDDC with x8-based memory modules.A minimal single-channel configuration of one 1 GB memory module perprocessor is also supported in this mode.Table 3-1 and Table 3-2 show sample memory configurations that follow theappropriate memory guidelines stated in this section. The samples showidentical memory-module configurations and their the physical and availablememory totals. The tables do not show mixed or quad-rank memory-moduleconfigurations, nor do they address the memory speed considerations of anyconfiguration.
