I know that dual channel increases performance a bit, but i was wondering if the dual channel kits they sell are really just two identical memory sticks, or if they are manufactured to work like dual channel?
Im asking this because im thinking of buying 2x4gb kit, then buying another, identical 2x4gb kit later when i get more memory. Can i do this, or should i just buy a 4x4gb kit right now?
just 2 closely matched sticks. two now, two later is fine. Many people do this. The first pair will be dual channel and the second pair dual channel, but it's not dual channel between pairs. Note though that if you get 2 completely different pairs eg 1 pair 1600 and 1 pair 1800, then you'll have to run a common timing which both pairs work at, but this won't affect dual channel.
The kits consist of 2 matched sticks that have been tested and verified to work together in dual channel mode. You can go with a 2x4 kit now, and another later, but you still want to match all of the sticks.
Best to get all at once in a single set, and if mobo supports it 2x8GB rather than 4x4GB, 2 sticks is less stress on the MC (memory controller) than 4 sticks. Also it's never a good idea to mix packages of DRAM, even the same exact model, those 4 stick packages you see that cost a few dollars more than 2 two stick packages, cost a bit more because of the testing, it's harder to pair up 4 sticks that all play nice than it is to pair up 2 sticks, also XMP programming is done by the packaged set, the advanced timings for a 4 stick set differ from a 2 stick set, i.e. a 2 stick set may call for a tRFC of 208 while a 4 stick set needs a 278 tRFC, another thing is the memory manufacturers guarantee packaged sets only, no guarantees for multiple sets
It's totally up to you, 2 sticks offer a very slight performance advantage, the difference is most telling with AMD where say for example a 8350 might be able to run a pair of 1866 sticks, yet if going 4 sticks it may only be able to run at 1600