4GB 2 X 2GB PC2-5300F 667MHz 240 pin DDR2 SDRAM ECC Fully Buffered FB DIMM Server Low Power Memory for HP Workstation XW8600 (PARTS-QUICK BRAND). Equivalent to HP Part Numbers: 397413-B21, 442823-B21,
4GB 2x 2GB DDR2 PC 4200 LOW DENSITY PC2-4200 533 MHz Desktop Memory RAM Non- ECC - Walmart.com
Kingston ValueRAM 4GB 667MHz DDR2 ECC CL5 DIMM (Kit of 2) Desktop Memory at Amazon.com