HP ML350 ISS Technology Update, Volume 8, Number 4 - Page 5

ISS Technology Update Volume 8, Number 4 Unbuffered DDR-3 DIMMs are a cost-effective solution for ProLiant G6 servers HP ProLiant G6 servers support Double Data Rate-3 (DDR-3) Synchronous Dynamic Random Access Memory (SDRAM) technology. DDR-3 SDRAM technology doubles the peak bandwidth of DDR-2 when operating at the same memory bus frequency. Memory manufacturers are producing two types of DDR-3 SDRAM DIMMs: Registered DIMMs (RDIMMs) and Unbuffered DIMMs (UDIMMs). ProLiant G6 servers support single-rank, dual-rank, and quad-rank RDIMM configurations. RDIMMs contain a register that buffers the address and command signals from the memory controller. The register also reduces the electrical load on the memory controller, allowing up to 3 DIMMs per channel (DPC), higher capacity per DIMM (2, 4, or 8GB), and faster bus speeds than UDIMMs. However, the register also increases the power requirements of each RDIMM by almost 1 Watt and adds 1 bus clock of latency. RDIMMs are identified with an R suffix in the module manufacturer's name (example PC3-8500R). Select ProLiant G6 servers support both single-rank and dual-rank UDIMM configurations. UDIMMs use less power and cost less than comparably sized RDIMMs; however, the capacity of UDIMMs is limited to 1GB or 2GB. ProLiant G6 servers that support UDIMMs, support a maximum of two UDIMMs per channel, which allows a maximum memory capacity of 24 gigabytes using dual-rank 2-gigabyte DIMMs. UDIMMs are a very cost-effective solution for servers with memory capacity of 24 GB or less. ProLiant G6 servers ship standard with RDIMMs, which are required to reach the maximum capacity of each server. Select ProLiant G6 servers support both RDIMMs and UDIMMs; however, RDIMMs and UDIMMs cannot be used together in a system. Customers should consider using UDIMMs when cost and power consumption are top priorities. HP simplifies memory selection by providing an on-line ProLiant Memory Configuration Tool (www.hp.com/go/ddr3memory-configurator) to help configure each server's memory and provide an orderable parts list. Table 1. Comparison between UDIMMs and RDIMMs in HP ProLiant G6 servers Table head UDIMMs RDIMMs Maximum speed supported DDR3-1333 DDR3-1333* Ranks per DIMM 1 or 2 1, 2, or 4 Maximum DIMMs per channel 2 dual rank DIMMs 3 dual rank DIMMs Maximum memory capacity 18-slot servers 24 GB 144 GB 12-slot servers 24 GB 96 GB *Maximum speed for quad-rank RDIMMs is DDR3-1067 Additional resources For additional information on the topics discussed in this article, visit: Resource Memory technology evolution: an overview of system memory technologies, 8th Edition DDR3 Configuration Recommendations for HP ProLiant G6 Servers URL http://h20000.www2.hp.com/bc/docs/support/SupportManual/c 00256987/c00256987.pdf ftp://ftp.hp.com/pub/c-products/servers/options/Memory-ConfigRecommendations-for-Intel-Xeon-5500-Series-Servers-Rev1.pdf 5