Why doesn’t 32-bit Windows support PAE correctly?
Here’s linux:
Linux 2.4.x does support greater then 4GB of physical memory (ie. RAM)
It does this by supporting Intel’s PAE (Physical Address Extension) features which are in all Pentium Pro and newer CPU’s.
It does this via indirect pointers to the higher memory locations, so there is a CPU and RAM hit for using this.
Benchmarks seem to indicated around 3-6% CPU hit just for using the PAE extensions (ie. it applies regardless of whether you are actually accessing memory locations greater then 4GB).
The PAE extensions allow up to a maximum of 64GB of physical memory that the CPU (not a process) can address.
PAE does not increase Linux’s ability for single processes to see greater then 3GB of RAM (see below).