PAE is crappy in a XMS sort of way if you want to use it to run applications that are able to access more than 4GB (3GB actually) of memory. However, if you just want to run multiple applications/processes that all require a large amount of Memory (say 1 or 2 GB) it has an advantage because it allows the system to keep each process' address space in physical memory. This fact is entirly transparent to the applications themselves. The application developer just "sees" the usual 32bit flat address space and does not have to jump through any XMS like hoops. With PAE you cant have processes use more than 4GIG of address space (unless you explicitly program for it like Oracle did for the PPro). Being able to keep multiple large process images entirely in physical memory can be of great benefit though for certain types of usage scenario.