I don't understand the output from top, ps or the columns in the Windows NT Task Manager. I don't understand the output from top, ps or the columns in the Windows NT Task Manager.
Any operating system has a fixed amount of physical memory available.
On operating systems, such as Windows NT, Windows 2000 or UNIX, the memory is logically divided in pages. When a page is not accessed for a long time, it is saved back to disk and discarded. If you look on the Windows NT Task Manager or the output from ps or top, Mem Usage is the working set size. It can be accessed without causing a page fault. This includes pages shared with other processes.