A-Tech 4GB Replacement for HP 708633-B21 - DDR3 1866MHz PC3-14900 ECC Unbuffered UDIMM 2rx8 1.5v - Single Server Memory Ram Stick (708633-B21-ATC) at Amazon.com
Crucial 4GB Single DDR3/DDR3L 1866 MT/s (PC3-14900) Unbuffered SODIMM 204-Pin Memory - CT51264BF186DJ at Amazon.com