On Nov 1, 2006, at 3:38 PM, Adam Goddard wrote: > To make a long question short, when they say that the ram limits of > logic (or any other software) are 4 Gigs, are they talking about > Real and > Virtual Memory combined? No, and the distinction isn't meaningful in any case. All address space is virtual; some of it happens to be mapped to real RAM. 32 bits of address space is 4GB, and so one process can have a 4GB virtual memory space. That 4GB is combined code and data, so very large programs have relatively less memory available for data. Further, Virtual Memory and Swap are not the same thing; the swap file is where writable RAM data goes to rest when RAM gets low. When you look at Activity Monitor, the Real Memory is the part of virtual memory that is actually mapped to RAM. Even on a system that has plenty of memory (and no swapping) you'll see large "virtual memory" usage, but this is pretty much entirely pointing at the applications' disk images; applications load by having the VM manager swap needed pages into RAM on demand. This makes applications load much more quickly, and leaves much more free memory. Effectively, each process has a map that says where each 4KB page of virtual memory lives. A page may be resident in RAM, or it may be in the swap file (if the system ran low on RAM and had to move some data out of the way), or it may be in the Applications folder (in the case of code), or it may not exist at all. Hope this helps... BTW, I suspect you have your numbers backwards; the VM number should always be greater than the real memory number.