HP ProLiant DL360e Configuring and using DDR3 memory with HP ProLiant Gen8 Ser - Page 5

• Number of ranks on the DIMM. Each rank on a memory channel adds one electrical load. As the electrical loads increase, the signal integrity degrades. To maintain the signal integrity the memory channel may be forced to run at a lower speed. • Number of DIMMs populated. The number of DIMMs attached to a memory controller affects the loading and signal integrity of the controller's circuits. In order to maintain signal integrity, the memory controller may operate DIMMs at lower than their rated speed. In general, the more DIMMs that are populated, the lower the operational speed for the DIMMs. • BIOS settings. Enabling certain BIOS features can affect memory speed. For example, the ROM Based Setup Utility (RBSU) in HP ProLiant servers includes a user-selectable setting to force memory to run at slower than rated speed in order to save on power consumption. See the section on BIOS settings for details. DDR3 DIMM types ProLiant Gen8 servers support three different DIMM types - Unbuffered with ECC Memory (UDIMMs), Registered Memory (RDIMMs) and Load Reduced Memory (LRDIMMs). UDIMMs and RDIMMs are familiar from their use in both G6 and G7 servers. However, LRDIMMs are a new class of memory that work solely with the HP ProLiant Gen8 architecture. Each type of memory has its unique characteristics, and the type of memory you use may depend on the application requirements for your server. Unbuffered DIMMs UDIMMs represent the most basic type of memory module. With UDIMMS, all address and control signals, as well as the data lines, connect directly to the memory controller across the DIMM connector. UDIMMs offer the fastest memory speeds, lowest latencies, and (relatively) low power consumption. However, they are limited in capacity. Unbuffered DIMMs with ECC are identified with an E suffix in the manufacturer's module name (example PC3L-10600E). UDIMMs are applicable for systems needing the lowest memory latency at the lowest power at relatively low memory capacities. Registered DIMMs Registered DIMMs (RDIMMs) lessen direct electrical loading by having a register on the DIMM to buffer the Address and Command signals between the DRAMs and the memory controller. This allows each memory channel to support up to 3 dual-rank DIMMs in Gen8 systems, increasing the amount of memory that a server can support. With RDIMMs, the partial buffering slightly increases both power consumption and memory latency. Load Reduced DIMMs Load Reduced DIMMs are available for the first time with the HP ProLiant Gen8 servers. LRDIMMs use a special chip to buffer all memory signals and to perform rank multiplication. The use of rank multiplication allows Gen8 systems to support 3 quad-ranked DIMMs on a memory channel for the first time. You can use LRDIMMs to configure systems with the largest possible memory footprint. However, LRDIMMs use the most power and have the highest latencies for the same memory clock speeds. Table 2 provides a quick comparison UDIMMs, RDIMMs and LRDIMMs for ProLiant Gen8 systems using the 2P Intel architecture. 5