The conceivable adress range is 4GB for a 32 bit word, but also some of the address range needs to be put aside for OS services, etc. and typically all of the major OS's simply split the address range down the middle, so that there's an upper and lower range, split at the 2GB mark, one half for services and the other half the (allocatable) data heap. So far as I am aware this applies to all Windows Mac OS's and UNIX brands. The only exception that I'm aware of was an enterprise version of NT which allowed 3GB for program data, so at least there is maybe some flexibility. At the end of the day though, OS developers really aren't interested putting in the work to allow more space for application data because there simply isn't any compelling reason as to why any program should need anything like 2GB of memory in the first place. Bill