4GB KIT (2 x 2GB) For HP-Compaq Pro Desktop Series 4000 (Small Form Factor) 6000 (MicroTower) 6000 (Small Form Factor). DIMM DDR3 NON-ECC PC3-8500 1066MHz RAM Memory. Genuine A-Tech Brand. 4GB KIT (2 x 2GB) DIMM DDR3 NON-ECC PC3-8500 1066MHz RAM Memory Genuine A-Tech Memory Lifetime Warranty Toll Free Technical Support 1-866-557-4527 Designed For HP-Compaq Pro Desktop Series. (See Compatibility List Below)