OS X and iOS Kernel Programming

Virtual Memory

The RAM in a computer system is a limited resource, with all of the running processes on the system competing for a share of it. When there are multiple applications running on a system, it is not unusual for the total amount of memory allocated by all processes to exceed the amount of RAM on the system.

An operating system that supports virtual memory allows a process to allocate and use more memory than the amount of RAM installed on the system; that is, the address space of a process is not constrained by the amount of physical RAM. With virtual memory, the operating system uses a backing store on secondary storage, such as the hard disk, to keep portions of a process address space that will not fit into RAM. The CPU, however, ...