Mac OS X Internals: A Systems Approach

Memoryspecifically, physical memoryis a precious resource in a computer system. An integral feature of modern operating systems is virtual memory (VM), whose typical implementation provides an illusion of a large, contiguous virtual address space to each program without burdening the programmer with details such as which parts of the program are resident in physical memory at any given time, or where in physical memory the resident portions are located. Virtual memory is commonly implemented through paging: An address space is subdivided into fixed size pages. When resident, each virtual page is loaded into some portion of physical memory. This portion, essentially a physical slot for a logical page, is called a page frame.