atomicWAR :
frostedtim :
Ivan, the simple answer to your question is: Get the 2x4 kit. This will make sure you can use dual channel mode.
Ignore all the other answers where they are telling you to just buy the additional stick, because MAYBE it will work.
First off you have some gall just saying ignore all other posts that don't agree with you. That is bad advice in general.
I am not arguing getting a dual channel kit will save some potential headaches, it will. And when I said same make model ram and specify same everything down to clock rate (cl) needs to be identical. Every spec must match ( speed, capacity, CL, all timings, voltage, memory chips used on the kit....everything) or mixed memory mode is a possibility and that is not a good outcome performance wise. All dual channel sets are, are two sticks guaranteed to play nice together. Something you don't get when buying the same exact identical ram. More times then not though if you do your homework and make sure everything is exactly the same, it is not a problem. So saying "MAYBE it will work" isn't right...most likely it will work just fine. Now if you don't get the exact same ram (same everything I mentioned early) then there is a lot of truth in your statement but I didn't encourage him to get kind of close ram where your statement would apply. Long story short, it is up to the OP if he wants to deal with a potential hassle (a very small potential if he purchases as I recommended and have done myself countless times over the last 20 years I have been building PCs) and save money or spend more money and save on a hassle that likely will never come. You never know that saved money could well be spent elsewhere. All that said if the OP cannot find identical make ram (again make model, speed, timings, CL, memory chips used) then he is better off getting a dual channel kit. If he can find the ram it would be worth it in my opinion to get it and save some money.
It was a simple answer to a simple question. And if you actually read ANY of what I had written, I was saying that for the purposes of ensuring dual channel mode worked, as intended, then go with the kit option.
You just had to go the full mega-nerd-fanboy route. Look, I didnt disagree that it was possible to find a matching stick for the existing one, but due to manufacturers making similar sticks with same specs and labeling, this makes things confusing for a lot of people. Im trying to be helpful to the OP. Long technical diatribes may work for fellow enthusiasts, but you tend to browbeat the technical specs to hard for most people.
My answer, for the OP's question is correct. Though the other answer might be correct, you have to be very sure you got the right module, otherwise its not going to work as intended. The RAM will still likely function, but not in dual channel mode, and the user may not even notice depending on his usage. Im not trying to wast the users time or money here.
The simple answer, the one that gives the least over all headache here, is for the OP to get the kit.