Arch Memory 4 GB (1 x 4 GB) 204-Pin DDR3 So-dimm for HP ProBook 4720s RAM Arch Memory is a Registered Trademark of Arch Computer, LLC 4GB 204-Pin DDR3 1333MHz SO-DIMM Compatible with systems that use 204-Pin PC3-10600 SO-DIMM modules 4GB Memory for HP ProBook 4720s by Arch Memory Lifetime Replacement Warranty