In computer operating systems, paging is a memory management scheme by which a computer stores and retrieves data from secondary storage for use in main memory. In this scheme, the operating system retrieves data from secondary storage in same-size blocks called pages. Paging is an important part of virtual memory implementations in modern operating systems, using secondary storage to let programs exceed the size of available physical memory.
For simplicity, main memory is called "RAM" (abbreviated from "random-access memory") and secondary storage is called "disk" (a shorthand for "hard disk drive"), but the concepts do not depend on whether these terms apply literally to a specific computer system.
The first memory "pages" were concepts in computer architecture, regardless of whether a page moved between RAM and disk. For example, on the PDP-8, 7 of the instruction bits comprised a memory address that selected one of 128 (27) words. This zone of memory was called a "page." This use of the term is now rare.
A pager (also known as a beeper) is a wireless telecommunications device that receives and displays numeric messages and/or receives and announces voice messages. One-way pagers can only receive messages, while response pagers and two-way pagers can also acknowledge, reply to, and originate messages using an internal transmitter. Pagers operate as part of a paging system which includes one or more fixed transmitters (or in the case of response pagers and two-way pagers, one or more base stations), as well as a number of pagers carried by mobile users. These systems can range from a restaurant system with a single low-power transmitter, to a nationwide system with thousands of high-power base stations.
One of the first practical paging services was launched in 1950 for physicians in the New York City area. Physicians paid $12 per month for the service and carried a 6 oz (200 g) pager that would receive phone messages within 25 mi (40 km) of a single transmitter tower. The system was manufactured by the Reevesound Company and operated by Telanswerphone. In 1960, John Francis Mitchell combined elements of Motorola's walkie-talkie and automobile radio technologies to create the first transistorized pager, and from that time, paging technology continued to advance, and pager adoption continued to expand, until the early 1990s. However, by the mid-1990s, as cellular technologies became cheaper and more widely available, advanced services began to displace paging as a commercial product. Today, pagers exist largely as niche products, finding preferential use in applications such as hospitals, public safety, and retail locations where their simplicity, high reliability, and low cost represent significant advantages.