well... people would not see more than roughly 4 gb ram used, if 5 wow instances could only use the 2-4gb ram range. so no one on these boards would have suggested to get more than 4gb ram.

the thing is: a 64bit operating system gives a range to the 32bit application, in which this application can address its needed memory. the addresses in this range can be addressed with 32bit addresses (2gb or 4gb range or whatever). the operating system is then the one responsible to readdressing to the real hardware addresses.

at least, that is how i think this works. but as my 12 gig ram are utilised quite good with 5 instances and not much more running, i'd say it is a safe guess, that what i described is what is happening.

on another note: any other way would possibly be pretty detrimental to sales numbers of 64bit operating systems and ram modules ^^

i'm not really sure about internals like this (just a dumb webdeveloper), but aren't 32bit applications in a 64bit windows running kind of in a virtual machine? not as in vmware or the like, but like in an emulated 32bit os?