[geeks] Greater than 4GB swapfile on XP...

[nate at portents.com]

> Hmm...so the question becomes is there any negatives to enabling it on a
> non NX/XD system.  For that matter are there many P4 or greater systems
> without XD/NX?

Well DEP is an extra security measure (which makes sure that only memory
that has been marked as executable can have code executed) which relies on
PAE and NX/XD, whereas PAE is a 36-bit addressing scheme (running in a
32-bit addressing environment) introduced back with the Pentium Pro.  As
you might imagine, you can't get 36-bits of addressing space in a 32-bit
environment without additional overhead.

I recommend reading this:

http://www.microsoft.com/whdc/system/platform/server/PAE/pae_os.mspx

Apropos quotes:

"PAE maps up to 64 GB of physical memory into a 32-bit (4 GB) virtual
address space using either 4-KB or 2-MB pages."

"During a remap operation, it is necessary to ensure that all processors
have valid logical-to-physical mapping on chip. Therefore, remap
operations require a TLB shoot-down, because the logical-to-physical
association is invalidated by the remap (where "logical" = the
application/process view of memory)."

"There is a performance impact while the processor (or processors) reload
the TLB. All operating systems have this issue..."

- Nate