I recently built a new computer. Fast processor, linux 64, 12G of ram. I wasn't sure if that much RAM was overkill or not. Here's what I'm finding:
I haven't rebooted in about 3 days. I have a bunch of stuff open that I use during my normal workday. Of the 12 G, 4.2 G is free. The rest is used by programs or cache. I don't have the HD set up for virtual RAM (using the hard drive as ram which slows down the fetching of data).
The conclusion I draw from this is that the system is using about 8G of ram. If you have less available ram, the OS will need to play games to work, which will slow your system down or possibly cause a crash. Since my other machine freezes with 4 G once a day, its apparent that for my use, the 4 G was not enough.
Anyway, just some observations.