Not sure if you have an OEM computer, but I had a Dell and tried to add 16GB (2x8) 1600mhz Vengeance RAM to existing 8GB OEM RAM. It only operated at 1333mhz vs. 1600 mhz. There are forum comments that certain performance RAM come this way despite their advertised max speed and then have to be tweaked in the BIOS. The Dell BIOS would not allow for RAM speed tweaking. I ultimately found 11CL value RAM to match the 11CL OEM RAM and now I have 24GB of RAM working at 1600mhz. IT has been working awesome for over 1/2 year now.