reads and writes were carried out on paired bits in this fashion. Applications Twistor was used in a number of applications. Much of the development funding was supplied by the US Air Force, as twistor was to be used as the main memory in the LIM-49 Nike Zeus project. In the United States the Bell System (American Telephone & Telegraph) also used twistors with permanent magnets as the "Program Store" or main memory in their first electronic telephone switching system, the 1ESS as well as others in the ESS series of electronic telephone switches, and did so up to the 4ESS switch introduced in 1976 and sold into the 1980s. In addition, twistor was used in the Traffic Service Position System (TSPS), Bell's successor to cord telephone switchboards which controlled call handling and coin collection for local and international calls. By 2017 all remaining TSPS and ESS installations used to provide telephone service in rural areas of the United States had been removed. Some systems may remain in use Mexico and Colombia, where many U.S. systems were sold and re-installed after being removed from service in the United States. References Citations Bibliography "Telephone exchange will keep calls 'in mind'", New Scientist, 5 November 1964, p. 344 External links Memory Units - a general discussion of computer memory systems written in the late 1960s, which includes a discussion of twistor. History of computing hardware Computer memory Non-volatile memory