SP-1 (Stored Program 1) was the name of a computerized

telephone exchange telephone exchange, telephone switch, or central office is a telecommunications system used in the public switched telephone network (PSTN) or in large enterprises. It interconnects telephone subscriber lines or virtual circuits of digital syste ...

(a so-called switching office) manufactured by Northern Electric (later Northern Telecom and now

Nortel Networks Nortel Networks Corporation (Nortel), formerly Northern Telecom Limited, was a Canadian Multinational corporation, multinational telecommunications and data networking equipment manufacturer headquartered in Ottawa, Ontario, Canada. It was foun ...

beginning in 1972) in

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tota ...

. It was introduced in 1971 (as stated in a Northern Telecom print ad that is included (page 55) in a history of Nortel, written by Peter C. Newman who was commissioned by Nortel to write it. Copyright is 1995. No ISBN.) As indicated by the name "Stored Program", the SP-1 introduced

computer control Computer Control Company, Inc. (1953–1966), informally known as 3C, was a pioneering minicomputer company known for its DDP-series (Digital Data Processor) computers, notably: *DDP-24 24-bit (1963) *DDP-224 24-bit (1965) *DDP-116 16-bit (1965) *D ...

to the telephone switching market. (AT&T's #1ESS preceded the SP-1 by several years.) A central computer controlled the operation of the switch. Switch behavior was determined by the operation of a computer program. With its use of computer hardware and software control, the SP-1 marked an evolutionary step in telephony design. It was an intermediate form between the previous generation of electromechanical systems and the next generation of fully digital systems. Like the previous generation of systems, the SP-1 was an analog switch that used a special form of mechanical relay (Minibar

crossbar switch In electronics and telecommunications, a crossbar switch (cross-point switch, matrix switch) is a collection of switches arranged in a matrix configuration. A crossbar switch has multiple input and output lines that form a crossed pattern of ...

) to provide the voice connections. The voice signal remained in the analog domain throughout the exchange, with the crossbar switches providing a metallic path to connect the end points of a call together. However the SP1 replaced the previous generation's complex relay-based controllers (

markers The term Marker may refer to: Common uses * Marker (linguistics), a morpheme that indicates some grammatical function * Marker (telecommunications), a special-purpose computer * Boundary marker, an object that identifies a land boundary * Marke ...

) with a modern

Harvard architecture The Harvard architecture is a computer architecture with separate storage and signal pathways for instructions and data. It contrasts with the von Neumann architecture, where program instructions and data share the same memory and pathways. ...

electronic computer, with separate data and program memories. SSI DTL logic was used throughout. Two types of memory was used - ferrite sheet memory for the CPU and

Piggyback Twistor Piggyback, piggy-back, or piggybacking may mean: Transport * Piggyback (transportation), something that is riding on the back of something else Art, entertainment, and media *Splash cymbal piggybacking, mounting a cymbal on top of an already s ...

memory for the storage of program and routing information. A number of variations on the base switch were available. A "two wire" version for local service, a four wire version for toll service. Two/four wire versions were also available as was a TOPS variant that was used to provide Operator services. The first four wire switch (four wire-tops, i.e., it provided toll switching and operator services) was placed in service in Thunder Bay circa 1972. The operator service consoles (CRTs) used an Intel 4004 processor. The next generation of systems evolved from the SP1 design to replace the analog switch with a digital technology. SP-1 proved the feasibility of software-controlled systems for telephony. It set the stage for the introduction of fully digital systems with the development of the DMS (

Digital Multiplex System Digital Multiplex System (DMS) is the name shared among several different telephony product lines from Nortel Networks for wireline and wireless operators. Among them are the DMS-1 (originally named the DMS-256) Rural/Urban digital loop carrie ...

s) by Nortel in the 1970s. (Nortel's SL-1 (PBX) was Nortel's first fully digital switching system, and it was introduced in service in 1975.)

See also