647909-B21-PCW is a HP Compatible 8GB PC3-10600 DDR3-1333 2Rx8 ECC 1.35v UDIMM (HP PN# 647909-B21). This is a 'major brand' module (from either Samsung, Micron, Hynix, Infineon, etc.), equivalent in every way to HP original memory. All PCW modules meet or exceed OEM specifications and JEDEC standards.
