Wintec ONE MHzCL9 4GB(2x2GB) UDIMM Kit 1.65V with HS 4 Dual Channel Kit DDR3 1866 (PC3 15000) 240-Pin SDRAM 3OH18669U8H-4GK 4GB (2x 2GB) DDR3 1866MHz RAM module; it lets you experience faster system performance 240-pin DIMM; it provides a much stable and smooth computing 2 memory modules; they share the number of system tasks among themselves, so one module doesn't get overcrowded