HP ProLiant DL980 DL980 G7 User Installation Guide - Page 41

Single-, dual-, and quad-rank DIMMs To understand and configure memory protection modes properly, an understanding of single-, dual-, and quad-rank DIMMs is helpful. Some DIMM configuration requirements are based on these classifications. A single-rank DIMM has one set of memory chips that is accessed while writing to or reading from the memory. A dual-rank DIMM is similar to having two single-rank DIMMs on the same module, with only one rank accessible at a time. A quad-rank DIMM is effectively two dual-rank DIMMs on the same module. Only one rank is accessible at a time. The server memory control subsystem selects the proper rank within the DIMM when writing to or reading from the DIMM. Dual- and quad-rank DIMMs provide the greatest capacity with the existing memory technology. For example, if current DRAM technology supports 2-GB single-rank DIMMs, a dual-rank DIMM would be 4GB and a quad-rank DIMM would be 8-GB. Although only one data rank is accessed at any given time for each DIMM, optimized command and address pipelining via various interleaving schemes enables the Intel® Xeon™ 7500-series processor architecture to benefit from dual-rank and quad-rank DIMMs. A dual-rank DIMM performs significantly better than its single-rank counterpart. A quad-rank DIMM provides further performance improvement even at the same DIMM capacity. DIMM identification To determine DIMM characteristics, use the label attached to the DIMM and the following illustration and table. Item Description 1 Size 2 Rank 3 Data width 4 Memory speed Definition - 1R = Single-rank 2R = Dual-rank 4R = Quad-rank x4 = 4-bit x8 = 8-bit 10600 = 1333-MHz Hardware options installation 41