1T or 2T, but that only available on nvidia chipset mobo, or maybe my intel 975 n my previous 965 can't let me select... to proper gain performance from oced ram, higher frequency with good close CAS latency is very important... ther r rams can do 800mhz with CAS3, team extreme for 1... n some manage to do 1000mhz with CAS4 with the same ram...