I upgraded WinXP Pro x64 partition to vista because... let me think...
Sure, 4GB was nice, but practically ZERO driver support for XP Pro x64

As for your comment about "Only server OS systems..."

I suppose it is known that the limit is 4gb on XP (why though?)
-- http://msdn.microsoft.com/en-us/library/ms791485.aspx

The 4GB limit is really just OS developers being lazy (or greedy?)
Truly, PAE / NUMA / 4GB limit is far more reliable on linux (lol)
.... What do I know; I'm just a developer that has vista for gaming.

My opinion, greed -- the 64 bit OS is unnecessary to access 4GB or more
of memory, but then you are EMULATING 32bit mode for gaming and other
apps. My very first thought was to check vista's "help and support" ...

1) go to your start menu and open "help and support" in windows vista.
2) type "PAE" in the search
3) the only result is "Physical address expansion (PAE) (definition)"

They even admit / explain it's "up to 64 GB" but didn't mention they
will deny you access to your ram / hold out and sell you "upgraded"
64bit version of windows to make an extra buck. Just my $0.02

JW wrote:
Only server OS systems can support more then 4GB of memory with a 32bit
OS since the use memory mapping to provide 4GB of logical memory to
different running process which map to different physical memory addresses.
Vista 32 bit like most if not all personnel computer Boss can not
address more then 4GB since it does not use memory mapping.