In addition, your new RAM wants 2.0V - 2.1V and old RAM more voltage at 2.2 - 2.25V. Whether this is an issue depends a lot on how much voltage you were already supplying it.
Was the old RAM showing at 800MHz and delivering the specs according to its SPD? And at under-voltage?
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Reply to SAINT19
It's not clear what you're asking. Are you considering buying both the 1066 and the 800 RAM and installing them both?
Or asking which to get or which can you run?
sorry bout that - im asking because I have just bought 2x2G of DDR2 1066 and already have 2x2G DDR2 800. I was wondering if its possible to run 1066 with 800 on the same motherboard - and have both run at full capacity
In addition, your new RAM wants 2.0V - 2.1V and old RAM more voltage at 2.2 - 2.25V. Whether this is an issue depends a lot on how much voltage you were already supplying it.
Was the old RAM showing at 800MHz and delivering the specs according to its SPD? And at under-voltage?
Oh I see now, maybe I should return the 1066 and grab 2x2GB of 800 for the best compatibility? Or do you think I should maybe grab another 4G of 1066 -- I do a lot of 3D modeling and gaming.
If the 1066 works fine with your existing 800, it's likely not worth the cost of returning the new RAM, paying re-stocking, new shipping, etc... I'd test it out and see how it does.
The difference in actual speed between 1066 and 800 RAM is very minor. Your old RAM had nice timings at 4-3-3-10 - if the 1066 will match that when running at 800, you're in fine shape.
Looking at your current setup with CPUz will give you the current timing conditions with only the old RAM in, compare that to its SPD (a chip in the RAM which tells the motherboard how to set the RAM - in theory!). The compare these when new RAM is installed together.