PAE помагает когда больше 4гб памяти.
Цитата
The PAE option provides support for the physical address extensions capa-
bility of the Intel Pentium Pro and above CPUs, and allows for up to 64
gigabytes of memory to be used in systems capable of supporting it. With
the PAE option, memory above 4 gigabytes is simply added to the general
page pool. The system makes no distinction between memory above or below
4 gigabytes, and no specific facility is provided for a process or the
kernel to access more memory than they would otherwise be able to access,
through a sliding window or otherwise.