HP DL360 Memory technology evolution: an overview of system memory technologie - Page 14

Lockstep memory mode Lockstep memory mode uses two memory channels at a time and provides an even higher level of protection. In lockstep mode, two channels operate as a single channel-each write and read operation moves a data word two channels wide. The cache line is split across both channels to provide 2x 8-bit error detection and 8-bit error correction within a single DRAM. In three-channel memory systems, the third channel is unused and left unpopulated. The Lockstep Memory mode is the most reliable, but it reduces the total system memory capacity by a third in most systems. Memory protection mode summary The Online Spare, Mirrored Memory, and Lockstep Memory modes enhance reliability and availability. A faulty DIMM does not have to result in unscheduled downtime. A server can remain up and running until it is convenient to take the equipment offline and down for servicing. However, memory protection modes do sacrifice performance. The reduction in available channels limits bandwidth and reduces a system's total capacity. Nevertheless, server availability is considered the highest priority for enterprise environments. The user configures the system for the desired memory protection mode through the ROM-based Setup Utility (RBSU) contained in the BIOS. Online Spare, Mirrored, and Lockstep memory protection modes are mutually exclusive, meaning that only one mode may be selected at a time. The memory sockets must be loaded with DIMMs that are identical in type, size and rank. 14