twajetmech

If your mobo supports running the memory in dual channel mode then you should use matched pairs of memory for best performance and compatability....to run in dual channel mode with all 4 dimm slots populated ideally you would have all 4 memory modules that are the same (2 sets of matched pairs) attempting to run 2 X 256 and 2 X 512 is hit or miss if it will work, your best bet would be to ditch the 2 X 256 and run the 2 X 512 and get another 2 X 512 when you can....since you are running Vista you'll appreciate the added gig of ram...Vista works well with just 1gig, but runs much better with 2gigs

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