Here is a good supplement just in:
Adding RAM is completely unrelated to the /3gb boot switch on 32-bit
Windows. Many people incorrectly assume that the /3gb boot switch lets
Windows use the installed RAM more efficiently.
If you’ve never had Pro/E crash because it tried to access more than 2GB
memory, then you don’t need the /3gb boot switch. This switch controls
how much virtual address space each process can address.
Virtual address space and RAM are not the same. A process’ virtual
address space exists both in RAM and on the hard disk (page file). The
Windows memory manager handles swapping memory pages to / from the disk
so that any memory pages required by the CPU are loaded into RAM.
So you can see that using or not using the /3GB switch has no effect on
how Windows uses the installed RAM.