Carol hits pretty close, but is still not 100% spot on the sugar.
32bit OSes can address 4GB of memory just perfectly, and with PAE that 32bit address space can be mapped to a "oh, I can't remember the bit amount, but it's more than you'll see in a single supercomupter node in your lifetime". Before SP1 of XP, you could get the full 4GB physical memory, too. After SP1, an arbitrary limit was introduced: Windows would no longer let you access more than the first 4GB
physical address space, even if this limit is insanely arbitrary. The official reason is that "drivers were too flakey, and too many 3rd party vendors ignored the HighPart of PHYSICALADDRESS structures"... which sounds a bit hollow to me, and most likely an excuse to get people to not run servers on non-server Windows versions.
But sure, morons like Creative have never been good at writing proper drivers, and there's been plenty of samples of people not supporting multi-CPU systems etc. So there definitely ARE 32bit drivers that won't work on systems with >32bit physical addresses. But PAE
itself isn't a problem, it's enabled by default to take advantage of per-page no-execute

Anyway, if it hadn't been for my
Vista Immersion experiment, I would have been a clean XP->Win7 user, and would have... mostly... loved it
