Doesn't PAE break the NX bit? - Data Execution Protection is more important. - No Win32 (std) process can allocate more than 2GB RAM anyway - Yes the other 2GB will be used, as you'll be running 80 or so processes (not processors) 'at once', plus the kernel.
32-bit Windows has smaller pointers, so for most apps (85%+) it's faster and uses less memory.
if i install only 4gb ram can i run 32 bit ?
You can or you could use 64 bit and get your whole ram
ok i will go for ultimate 64 bit ,by the way is it good for gaming ?
Yes. It is superior in pretty much every way.
I wouldn't spend the extra money on Ultimate for gaming (although I sense a torrent initializing...).