Re: memory question
I've heard/read bad things about PAE, including a diatribe from Linus Torvalds. If they're right, then fortunately enough I haven't ever had to use it.
Yes, 32 bit systems are limited to 4G unless they have some scheme for accessing more, such as PAE.
I'm running 12G on a 64-bit system. If I don't have any VMs running then I don't often get above 4G used. I have managed to run out of 6G, just barely. I used it as an excuse to double it, but the thing is I was using all sorts of tmpfs so part of that was the tmpfs. 64-bit systems are supposedly more memory hungry than a 32 bit system.
If you use a large database under heavy load, or virtual machines, or some other service that takes huge memory, then you can run out of 4G. You would have had to install whatever it is deliberately, I don't know of anything installed on a generic system that does that without you knowing about it.
Help stamp out MBR partition tables. Use GPT instead!