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I have a server with 4 DDR2 RAM slots. I just bought 2x2GB 800MHz sticks for it, for a total of 4GB RAM. I also have 2x512MB 677MHz sticks left over.

Is it better to use the 2x2GB sticks at 800MHz totaling to 4GB, or use the 2x2GB sticks plus the 2x512MB sticks at 677MHz totaling to 5GB?

Is the extra 1GB of RAM worth the speed loss from 800MHz to 677MHz?

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I'd go with the extra RAM, simply because RAM is so much faster than hard drive. You're reducing the amount of drive necessary for paging out the memory. – user3914 Mar 1 '11 at 2:28
That slight change in speed will hardly be noticeable compared to the gain of 1 GB of RAM. – MaQleod Mar 1 '11 at 3:09
Watch out for stability issues if you run different RAM types at once. Although it shouldn't occur, I find very often that mixing RAM leads to odd stability issues here and there. Usually less of an issue on server units, but still an issue. – Chris Thorpe Mar 1 '11 at 3:27
So it looks like ill use the 5GB of RAM. Thanks! – lanrat Mar 1 '11 at 3:49
up vote 4 down vote accepted

If you are short on memory, go with 5 GB, but if your swap is always empty at 4GB and you have applications that benefits from memory transfer speed, use the higher speed. In most cases you won't notice a difference between 667 and 800 MHz though, I guess.

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I'd also go with the extra RAM for the same reasons that Randolph listed. The RAM is ECC, I hope? A final answer would depend on what the server is being used for. Almost anything would like more RAM over the speed of RAM, but then again, there's those weird instances where that little bit of speed difference truly does matter. Me? But me? I'd (almost) always go with more RAM.

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