I wouldn't bet that NT supports 2GB of RAM - they used to have a 2G/2G
user/kernel virtual memory split, but I'm told the new NT's do (or are
expected to do) the same thing as Linux - 3G/1G.
Yes, you can get at more memory than the kernel mapping can hold at one
time, but it is very seldom worth it: it makes just about everything
slower. Especially as there are much better alternatives available
already (they may not be from intel, but as you won't be running Word in
2+GB of RAM anyway who cares?)
I doubt the 36-bit physical extensions are very usable on general-
purpose setups, and I strongly suspect that the main reason intel added
them was that (a) it was easy to do (much easier that extending your
virtual address space) and (b) they wanted it for their supoercomputer.
(And (c) they could start looking at how the eventual 64-bit page tables
would end up looking on the P7, but I sincerely hope that they quickly
noticed that there are better way of doing it than the braindamaged page
table tree that the P6 extended mappings seem to indicate).
Linus