Page (computer Memory)

Page (computer Memory)

A page, memory page, or virtual page is a fixed-length contiguous block of virtual memory, and it is the smallest unit of data for the following:

• memory allocation performed by the operating system for a program; and
• transfer between main memory and any other auxiliary store, such as a hard disk drive.

Virtual memory allows a page that does not currently reside in main memory to be addressed and used. If a program tries to access a location in such a page, an exception called a page fault is generated. The hardware or operating system is notified and loads the required page from the auxiliary store automatically. A program addressing the memory has no knowledge of a page fault or a process following it. Thus a program can address more (virtual) RAM than physically exists in the computer. Virtual memory is a scheme that gives users the illusion of working with a large block of contiguous memory space (perhaps even larger than real memory), when in actuality most of their work is on auxiliary storage (disk). Fixed-size blocks (pages) or variable-size blocks of the job are read into main memory as needed.

A transfer of pages between main memory and an auxiliary store, such as a hard disk drive, is referred to as paging or swapping.