This HP 500660-B21 compatible 4GB () DDR3-1066MHz quad rank registered ECC 1.35V 240-pin CL7 factory original RDIMM kit is 100% guaranteed to be compatible with your system and to work right the first time. All of our server memory is built to strict JEDEC standards at one of the tier 1 facilities (Samsung, Micron, or Hynix). Our products are also guaranteed by federal law to not affect or void OEM warranties.