Confused about RAM memory upgrade

[DiscoStu]

I want to upgrade the performance of my PC and the obvious thing to do is add more RAM. I know what I need but I'm reading conflicting info on different sites. I need DDR RAM but I've read that with DDR you MUST install a matched pair of RAM sticks, ie if I want to have 1GB of RAM then I have to install 2 x 512kb sticks. But how can this be true if I currently only have ONE RAM stick in my machine, and always have done? Surely I should have 2 x 256kb rather than the single 512kb that I actually have?
I'm planning on buying a single 1GB DDR 3200 400mHz stick to add to my current 512kb. Will this work ok?

[ChuckFickens]

if your computer takes DDR 3200 400mHz ram buy one 1gb stick of that spec put it in it will work fine..

[lajohn]

Marc you are such a genius!
Could you answer my question also? x

[ChuckFickens]

only if you spell my name right (or preferably stop using it on here altogether)!

[lajohn]

cool. spelling was the disguise :-)

[rojash]

If you install a pair they must be matched - that's not quite the same as you must install a matched pair - geddit?

[fo3nix]

Install a pair that match --- means that you must use two of the same types of RAM (both DDR, etc.). This is a must.

Matched pair: optional. On some newer systems (last few years), having a matched pair (1x1GB etc.), you get greater performance as two memory channels can be utilised at once.

Goto crucial.com/uk and scan your system. It'll tell you what you can buy. You don't have to buy from Crucial, but they do make some of the best memory.