brianjay0914 :
My motherboard is "msi 970 gaming" , so if i buy 1x4gb today and 1x4gb in the other day and put it on the matching slot it'll be dual channel ?
The catch with buying DIMMs separately is that you have to be certain they are both built exactly the same way to enable full dual-channel operation. Otherwise, you end up in "interleaved" mode instead which is not quite as good or sometimes might not work at all.
This is why buying DIMMs in pair kits is strongly recommended since it eliminates the headaches and pitfalls associated with attempting to match DIMMs after-the-fact if you can no longer get another of the exact same model by the time you need it.