Hmm, good help is hard to find these days huh?
YES - of course you can add another Gig. No, it won't stop dual channel operation of your RAM. Dual channel brings far morre BANDWIDTH, not more SPEED. There is an important distinction. Dual channel = 6.4GB/s, single channel = 3.2GB/s. (This is where the 3200 part of "PC3200" comes from - it's capable of 3200 MB/s - divide this figure by 8 to arrive at the operating frequency, in this case, 400MHz (200 x 2).
There are a couple of provisos however: you **may* experience more latency (i.e. less speed) by adding 2 more sticks of RAM - some (repeat, SOME, not all) motherboards have slightly worse performance in latency, when the full number of slots are populated with RAM. You should also attempt to get identical RAM, or at least RAM with identical specs. I assume you are running the RAM by SPD, and are not overclocking.
Necessary to recall that SPD drops to the lowest common denominator of all four sticks - so do NOT buy slow RAM.
You sound like me when I was younger...heh, those were the good days....
Adding more sticks of Memory
can drop Dual-Channel, depends on how many sticks. If the motherboard has 4x DIMM's and you put 3 in, bye-bye Dual-Channel. If you use all 4x DIMM's, and they are Dual-Rank modules (meaning there is RAM chips on both sides of the stick) than you cannot run 1T because the A64 memory controller can only handle 4 ranks in Dual-Channel. Now, there is something I have experienced, if you use 3 sticks, and 1 is Dual-Rank and 2 are Single-Rank, you
can run Dual-Channel with that.
Yes, all RAM will drop to the slowest (e.g., if you have 2 sticks and 1 is PC3200 and 1 is PC2700, you now have 2 PC2700, yay!). Dual-Channel is where the mem controller grabs from both sticks @ once, so a latency is possible and present, but not noticable.
No, you don't divide 3200 by 8 to get 400MHz operation (though it works out). You take the 400MHz operation and multiply it by 128 (Because Dual-Channel uses 2 64-bit interfaces) and divide THAT by 8 to get 6400MB/s (The speed of Dual-Channel).
~~Mad Mod Mike, pimpin' the world 1 rig at a time