Adding More RAM, What's Important?

I'm going to buy 4GB of RAM so I'll have a totaly of 6GB, and I'm just wondering if I need to have the exact same brand and timings as I do now. Do I need to get another set of Kingston HyperX RAM DIMMs, or can I get some from Gigabyte as long as they have the same timings and cas latency?

Usually two different brands will work in dual channel mode. There is a chance that they could not, but it will still run fine just not in dual channel mode. Chances are it will all work fine though. I have 2x512mbs of Wintec ram and 2x512mbs of kingston value ram in my back up rig. They are not the same speed and they run in dual channel it just all runs at the lower speed.

Ditto what Bob said. I have mixed different brands having different timings and discovered that they played well together! Your results may vary, though. But if the exact same brand was available for sale at a reasonable price I would definitely go that route first.

The key is to make sure they are simialr in speeds, theres no point in buying faster ram, since it will run at the same speed as the slowest ram module.  Also, with speed, if you already have 800mhz ram, there is no point in buying 1066mhz since it would run at 800mhz.

indeed as stated above, they will run at the slowest of the ram speeds... so ideally if you can get the same or similer ones that best.

Right right.... Actually I remember reading that my motherboard has some feature that'll allow two speeds of RAM to run... Either way, I've got 1066Mhz, so it's all good and fast. How much of a difference will I see if my RAM runs as 5-5-5-18 instead of 5-5-5-15 like it's supposed to??? From the tests I saw the only difference as far as speed is concerned is seen in games, so was I in the wrong by going with DDR21066 instead of 800?

Iain:

How much of a difference will I see if my RAM runs as 5-5-5-18 instead of 5-5-5-15 like it's supposed to???

My guess is that the difference would be neglible.

Of course you could always benchmark it, Iain! Super Pi is a great program, if you have never used it, and it is free. Slap-in that memory at 5-5-5-18 timings and run Super Pi a few times at the 1M setting (most popular). If it completes the run without errors it is stable. Now manually change the timings to 5-5-5-15 and run the same test to see how much your time improves. If that is successful, try 4-5-5-15 and see what happens. The worst that can happen is that it won't boot or it will bluescreen. If you run into instability problems try bumping the RAM voltage just a bit above OEM. 

thents of a second if that...

No there is no issue of same brand. The matter is that both the RAM should be identical in frequency. If the frequency matches the stabillty will there.

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Rikin