If the CPU is not fully 64 bit, then it will only use (not see) 4GB
of
memory. After completing overhead actions this leaves something in
Nope. An x86 processor with PAE can be 32bit but can address 36bits of
address space (just not directly all at once). This needs a lot of
management and if you add a lot of memory to a 32bit box it spends more
and more of its time changing which memory it is looking at.
the range of 3.5 GB for the Operating System and other
applications....
Adding more memory than this limit will not result in better
performance and may actually make matters worse.
If the board supports it. It can indeed often reduce 32bit performance
that kicks in well below 4GB however because of the need for mappings of
hardware space, user space and kernel. More than 900MB or so starts to hit
it and by 2GB its having measurable impact. Above 4 you really want 64bit.