Page address register
Encyclopedia
A page address register contains the physical address
Physical address
In computing, a physical address, also real address, or binary address, is the memory address that is represented in the form of a binary number on the address bus circuitry in order to enable the data bus to access a particular storage cell of main memory.In a computer with virtual memory, the...

es of pages currently held in the main memory of a computer system. PARs are used in order to avoid excessive use of an address table in some operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...

s. A PAR may check a page's number against all entries in the PAR simultaneously, allowing it to retrieve the pages physical address quickly. A PAR is used by a single process
Process (computing)
In computing, a process is an instance of a computer program that is being executed. It contains the program code and its current activity. Depending on the operating system , a process may be made up of multiple threads of execution that execute instructions concurrently.A computer program is a...

 and is only used for pages which are frequently referenced (though these pages may change as the process's behaviour changes in accordance with the principle of locality
Locality of reference
In computer science, locality of reference, also known as the principle of locality, is the phenomenon of the same value or related storage locations being frequently accessed. There are two basic types of reference locality. Temporal locality refers to the reuse of specific data and/or resources...

). An example computer which made use of PARs is the Atlas
Atlas Computer (Manchester)
The Atlas Computer was a joint development between the University of Manchester, Ferranti, and Plessey. The first Atlas, installed at Manchester University and officially commissioned in 1962, was one of the world's first supercomputers, considered to be the most powerful computer in the world at...

.
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