Kingston 4Gb DDR2-667 server/workstation memory with ECC Registered error correction, a 240-pin module built for a specific older-generation server or workstation platform rather than a modern consumer build. Dual-rank design with parity checking helps catch and correct memory errors in always-on server workloads, where an uncorrected bit-flip is a much bigger problem than on a desktop PC. Best suited to maintaining or upgrading an existing system already on this memory generation, not a new build.