Mix and matching RAM in Optiplex 780 SFF?

[littleninjasoccer]

Can two different 4GB RAM kits (two 2GB RAM sticks in each kit) go into the same computer (Optiplex 780 SFF)?

The Optiplex 780 SFF has 4 RAM slots and a max RAM capacity of 8G, the mix and matching part is what concerns me the most

 

[william p]

They need to be low density RAM aka X64 to run in the Dell. The thing is the RAM will run at 1066 speed in that system even if it's DDR3 1333, or 1600. The timings will be different than what's listed due to that. My 1333 CL9 modules run at 1066 CL7 in my Opti 380 due to this. These timings aren't published so It's hard to tell what will actually happen when you mix them. My advice is go to Crucial.com and get what they offer for that system. They guarantee compatability and have a lifetime warranty. BTW that system supports 16GB RAM. 4GB modules weren't available when that was sold so Dell doesn't list them in the spec. So you could pick up a pair of 4GB matching modules if you want to be sure.