I only have a vague idea of what dual channel is. Do all motherboards support it? If not, does it still make sense to avoid sticking in RAM of different sizes (but same frequency)?Let's say I get 2 x 1GB, and sell/return the 512MB. The 256MB came with the PC so I have to keep it, but would it be better if I set it aside and don't put it in the motherboard, and only use 2GB? In other words, frequencies being the same, is it better to have (2 x 1GB) or (2 x 1GB and 1 x 256MB)?