I'm looking for CAS2 512MB DDR400. Ideally known compatible with the Asus A7N8X-E Deluxe board, but I think I'll have to take my chances there.

The best I can find are either single sticks of 1GB in size or more at CAS2, or CAS 2.5 512MB.

The board can't handle more than a gig per slot, and it can't handle 2x 1GB DDR400. The highest combination it can handle in DDR400 is 2x512MB + 1x1GB, which achieves dual channel (though how exactly I'm not sure, CPU-Z agrees that my system is running in dual channel).

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My PC spec

Is there a known significant difference in the performance between the CAS 2 and 2.5?

I ask because there seemingly would be very little difference and as such why not just go with the 2.5 stuff that you've found?

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Fantom Thrust - SHW Battlebot
Dell M6300 - loaded
Dell M6700 - loaded
X1 X2 X3 X4 X5 X6 X7 X8 X9

I did in the end. There's "a bit of a difference" between CAS2 and 2.5. Sometimes performance tweaking involves taking what you can get, every inch of it

I wouldn't have paid a load more money for CAS2 over 2.5, but the option would have been nice on an ageing machine.

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My PC spec

I hear what you're saying and I've done the same in the past myself.

However lately and because my machines other than my M6300 laptop are so old, I've resigned them to the graveyard. I'm not putting another dime into any of them. I'm on a path to build a new machine in the spring of '10 after Intel releases its next chipset (the name escapes me at the moment...). DX11 will be out by then as well (in full force).

I probably ought to sell them before they completely devalue... ...the pieces worthwhile anyway...

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Fantom Thrust - SHW Battlebot
Dell M6300 - loaded
Dell M6700 - loaded
X1 X2 X3 X4 X5 X6 X7 X8 X9