The dual channel memory is used by socket 775 , 1156 ,1155.
Tri channel is used by socket 1366.
Quad channel is used by socket 2011.
AMD use just dual channel.
The diference is how the RAM is used by the system depending on socket in what is used.
Dual,triple and quad channels are the no of channels that can active and make data flow from the RAM module to the CPU(IF the cpu has memory controller in it- most of cpu in these days have it) at the same time. So you can find it as similar colour Ram Slots in your MB. For using dual , Triple and quad channel Ram you need exactly same Ram modules like 2 ,3 and 4 no of modules respectively.
No you can't buy different sets, if , you mean one set dual channel and one set tri or quad channel.
I mean 2 different sets of (2x4) with the same frequency. But I'm wondering this because I have an msi p67a gd80 that has dual channel memory but I got a 12gb vengeance set as a present and that's triple channel. That won't work will it? ...since its triple channel. I would have to buy a new set that was dual channel for it to work wouldn't I?
Nope, I changed it(My Reply) , it's worth the try since I'm not too sure, a triple channel set of RAM will work in Triple channel only with 3 Sticks of the same inserted. If 2 were inserted from the set, I think Dual Channel would be possible. Use 2 sticks from your older RAM and use 2 sticks from your new RAM put each set in the like colored slots and see if it shows up in the BIOS.
If it does, boot into windows and check with CPUz as to what it says about your RAM. If possible post a screenshot of the CPUz Memory Tab and 2 Screens of the SPD tab with each different Memory Selected in there.