AddOn 4GB DDR3-1333MHz UDIMM for HP VH638AA - DDR3 - module - 4 GB - DIMM 2

This HP VH638AA compatible 4GB DDR3-1333MHz Dual Rank x8 Unbuffered 1.5V 240-pin CL9 UDIMM is 100% guaranteed to be compatible with your system and to work right the first time. Adding additional memory is the best way to increase the performance of your system. All the memory is built to strict JEDEC standards to meet or exceed the Tier 1 OEM's factory requirements. The products are also guaranteed by federal law to not affect or void OEM warranties.