The system memory is installed on memory riser (MR) cards. The system requires eight MR cards for a four-CPU configuration and four MR cards for a two-CPU configuration (Each processor has two assigned MR cards). MR cards contain twelve DIMM slots, four DDR3 channels, and two memory buffer ASICs. Each memory buffer has two channels (A and B) and links to three DIMM slots per channel. Each memory buffer is connected to the processor's built-in memory controller by an SMI-2 link.
For balanced performance, each channel for each memory buffer on the MR card must be populated. The only exception supported is a minimum orderable configuration of two 16 GB DIMMs in channel's A and B of memory buffer 0.
For more information about MR cards, and memory layout, including guidelines for populating cards and DIMMs, see: Memory Riser Card and DIMM Reference