I upgraded the RAM on my early 2011, 13" Macbook Pro from 4 GB to 16 GB recently. The MBP never had problems and is now even better. I upgraded only because I found a great deal for RAM as well when purchasing an SSD.
When the MBP is idle, I am curious from looking at the "Memory Used" in Activity Monitor, why has the usage gone up from an average about 2.5GB to about 4.5 GB with more memory available?
Could it be that the MBP required more memory earlier as well, just that it used less RAM and more Swap? Wouldn't the Swap be used only after the entire 4GB would have been used, earlier?
(I did not notice the Swap usage earlier - but now that I have, after the upgrade, it is always zero)
Answer
You are on the correct track with RAM and SWAP, but not 100% correct. Most OS's will see unused RAM and use it to cache recent disk requests, eating up free RAM (which can be released at a moments notice) to give you a possible IO speed increase.
[ Even a system with a lot of RAM might still write to swap if the bits in RAM are not being accessed and the OS recons other things are more likely to be recalled ]
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