They are just designated either single, dual, tri, or quad channel because they are specifically tested in that configuration together to work. So, all 4 sticks in a quad channel set are just normal RAM that have been tested in sets of 4. That's why generally, you want to buy your RAM all at once, because a set of 2 sticks have been tested and confirmed to work together, although obviously this is not always economical or possible, but it gives you the best chance of having no issues.