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The IBM 1750, 2750 and 3750 Switching Systems were telephone exchange systems produced by IBM from the 1960s to the 1990s. IBM engineers in the
IBM La Gaude The IBM La Gaude Study and Research Center (Centre d'études et recherches IBM La Gaude) was a computer research laboratory for IBM, located in La Gaude near Nice on the Côte d'Azur. In the 1990s, it became a presentation center for IBM Business ...
Research Laboratory, north-west of
Nice Nice ( , ; Niçard: , classical norm, or , nonstandard, ; it, Nizza ; lij, Nissa; grc, Νίκαια; la, Nicaea) is the prefecture of the Alpes-Maritimes department in France. The Nice agglomeration extends far beyond the administrative c ...
in
France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans. Its metropolitan ar ...
, developed an electronic Private Automatic Branch Exchange: the first stored-program-controlled PABX to be marketed and installed in the world. The product family handled up to 2516 extensions and 356 trunk lines. They were among those very few IBM products to be still in use in five European countries for some 40 years following the 1969 market introduction of the IBM 2750 Switching System. Before 1969 only
electromechanical In engineering, electromechanics combines processes and procedures drawn from electrical engineering and mechanical engineering. Electromechanics focuses on the interaction of electrical and mechanical systems as a whole and how the two system ...
Strowger and Crossbar PABXs were available. The family of IBM 1750, 2750 and 3750 Switching Systems was developed from the
IBM 1800 The IBM 1800 Data Acquisition and Control System (DACS) was a process control variant of the IBM 1130 with two extra instructions (CMP and DCM), extra I/O capabilities, 'selector channel like' cycle-stealing capability and three hardware index regi ...
. Each system included twin stored-program controllers (each with 32K or 64K main storage}; some 600,000 lines of code; emergency and every-night automatic switchover; twin disks (none for the 2750); and
solid-state Solid state, or solid matter, is one of the four fundamental states of matter. Solid state may also refer to: Electronics * Solid-state electronics, circuits built of solid materials * Solid state ionics, study of ionic conductors and their ...
switching.
Extension Extension, extend or extended may refer to: Mathematics Logic or set theory * Axiom of extensionality * Extensible cardinal * Extension (model theory) * Extension (predicate logic), the set of tuples of values that satisfy the predicate * Ext ...
, trunk and tie lines were connected by discrete
transistors upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink). A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch e ...
on plug-in panels. All systems were assembled in IBM's French Montpellier factory for France, Germany, Italy, and the UK.


Early development

The French engineers in
IBM La Gaude The IBM La Gaude Study and Research Center (Centre d'études et recherches IBM La Gaude) was a computer research laboratory for IBM, located in La Gaude near Nice on the Côte d'Azur. In the 1990s, it became a presentation center for IBM Business ...
in the late 1960s developed a prototype system based on the IBM 1130 to handle 500 telephone extensions and some 20
trunk lines In telecommunications, trunking is a technology for providing network access to multiple clients simultaneously by sharing a set of circuits, carriers, channels, or frequencies, instead of providing individual circuits or channels for each clie ...
to the local
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 ...
. They then developed the marketable IBM 2750 Switching System, code named Carnation, with IBM 1800 computers – two 1800s for fail-safe redundancy – each with 32K or later 64K of
magnetic-core memory Magnetic-core memory was the predominant form of random-access computer memory for 20 years between about 1955 and 1975. Such memory is often just called core memory, or, informally, core. Core memory uses toroids (rings) of a hard magneti ...
, and
IBM Solid Logic Technology Solid Logic Technology (SLT) was IBM's method for hybrid packaging of electronic circuitry introduced in 1964 with the IBM System/360 series of computers and related machines. IBM chose to design custom hybrid circuits using discrete, flip chi ...
(SLT), but no disks (disk storage was new and very expensive then). Maximising reliability, each
central processing unit A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, an ...
had its own transistorised switching network with crosspoint switching. The 2750 was greatly influenced by the European national telephone authorities ( PTTs) who insisted on isolating-line transformers to protect their engineers. The 2750 had large 40cm-by-30cm plug-in extension packs each handling only four telephone extensions with standard PTT 50-volt telephones. The Assembler-language program was loaded using punched paper tape, needing some 90 minutes for each of the two CPUs. Smaller maintenance programs could be loaded into unprotected storage. Fault finding was limited to 4K programs and needed an oscilloscope — but the 2750 was reliable enough to run 24/7. An attached
IBM Selectric typewriter The IBM Selectric typewriter was a highly successful line of electric typewriters introduced by IBM on 31 July 1961. Instead of the "basket" of individual typebars that swung up to strike the ribbon and page in a typical typewriter of the perio ...
let customers change system facilities such as the extension numbers of telephones of repositioned staff. The 2750 was very quiet as it was transistorised with no moving parts other than the cooling fans in the cabinets, compared with the noisy, electro-mechanical Strowger
PABX A business telephone system is a multiline telephone system typically used in business environments, encompassing systems ranging in technology from the key telephone system (KTS) to the private branch exchange (PBX). A business telephone syst ...
systems then everywhere across Europe.


Countries, costs, installations, 1968 to 2010

The 1968-available 2750 was sold in
France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans. Its metropolitan ar ...
,
Germany Germany, officially the Federal Republic of Germany (FRG),, is a country in Central Europe. It is the most populous member state of the European Union. Germany lies between the Baltic and North Sea to the north and the Alps to the sou ...
,
Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical ...
, and
Belgium Belgium, ; french: Belgique ; german: Belgien officially the Kingdom of Belgium, is a country in Northwestern Europe. The country is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeast, France to ...
; 3750s (from 1970) and 1750s (from 1979) were sold in these four countries and the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...
. In the UK a 2750 was installed in the IBM Wigmore Street, London office; another was in IBM's plant in Havant, Hampshire: this was used for demonstrations and by the employees at the plant. The
Netherlands ) , anthem = ( en, "William of Nassau") , image_map = , map_caption = , subdivision_type = Sovereign state , subdivision_name = Kingdom of the Netherlands , established_title = Before independence , established_date = Spanish Netherl ...
installed some in IBM sites. Costs ranged from $150,000 to $600,000, plus up to $60,000 for the 3750's large room, air conditioning, and false flooring because of the extensive cabling between the three 3750 cabinets. By the time the 1750 was withdrawn from sales in 1988, there were some 300 systems installed in Europe. 1750s and 3750s were still in use in the year 2010 -- some of the longest-life IBM products.


Functions new to markets

Long-distance and particularly international telephone calls were still very expensive in the 1970s. Although the 3750 when first marketed in 1970 cost almost double the equivalent-sized non-stored-program machines, the business case was compelling because the number of telephone operators could be halved, and for the first time organisations could determine what calls were made, where they were made to, and who made them. Suddenly the phone bill, instead of being a single item, could be allocated to departments and individuals, with details of called numbers and duration. However, systems were mostly ordered because of the first-time use of touch-tone telephones, call re-routing, short-code dialling etc (see below) — all functions taken for granted today.


UK sales

In the UK, the first 3750 customer was
British Caledonian British Caledonian (BCal) was a British private independent airline which operated out of Gatwick Airport in south-east England during the 1970s and 1980s. It was created as an alternative to the British government-controlled corporation airlin ...
Airways, quickly followed by Bland Payne Insurance Brokers,
Derbyshire County Council Derbyshire County Council is the upper-tier local authority for the non-metropolitan county of Derbyshire, England. It has 64 councillors representing 61 divisions, with three divisions having two members each. They are Glossop and Charlesworth, ...
and
Geest Geest is a type of landform, slightly raised above the surrounding countryside, that occurs on the plains of Northern Germany, the Northern Netherlands and Denmark. It is a landscape of sandy and gravelly soils formed as a glacial outwash plai ...
Bananas. Later many household names installed 3750, such as Great Universal Stores,
Grosvenor House Hotel ] JW Marriott Grosvenor House London, originally named the Grosvenor House Hotel, is a luxury hotel that opened in 1929 in the Mayfair area of London, England. The hotel is managed by JW Marriott Hotels, which is a brand of Marriott Internation ...
, Rowntree's, Rowntree Mackintosh,
Selfridges Selfridges, also known as Selfridges & Co., is a chain of high-end department stores in the United Kingdom that is operated by Selfridges Retail Limited, part of the Selfridges Group of department stores. It was founded by Harry Gordon Selfridg ...
,
Kwik Save Kwik Save is a British convenience store chain. Prior to 2007, it was also a discount supermarket chain that had shops across the United Kingdom. It went into administration in July 2007, but was brought back in April 2012. Its shops were sm ...
,
American Express American Express Company (Amex) is an American multinational corporation specialized in payment card services headquartered at 200 Vesey Street in the Battery Park City neighborhood of Lower Manhattan in New York City. The company was found ...
,
Mobil Mobil is a petroleum brand owned and operated by American oil and gas corporation ExxonMobil. The brand was formerly owned and operated by an oil and gas corporation of the same name, which itself merged with Exxon to form ExxonMobil in 1999. ...
(a network including 1750s on
North Sea The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian S ...
oil and gas platforms), Unigate (dairies),
Royal Bank of Scotland The Royal Bank of Scotland plc (RBS; gd, Banca Rìoghail na h-Alba) is a major retail banking, retail and commercial bank in Scotland. It is one of the retail banking subsidiaries of NatWest Group, together with NatWest (in England and Wales) ...
, Reckitt & Colman, Tesco, CWS (Co-operative Wholesale Society), and
Greater Manchester Police Greater Manchester Police (GMP) is the territorial police force responsible for law enforcement within the metropolitan county of Greater Manchester in North West England. , Greater Manchester Police employed 6,866 police officers, 3,524 mem ...
(GMP) — GMP installed a 3750 at their headquarters Chester House, and later a network of 1750s around the Greater Manchester area.


Systems

The systems all had both voice and data functions. Early-1970s computers had hardly any typewriter-like terminals and certainly no screens – the IBM Switching Systems introduced the novelty of simple digital-data capture from every touch-tone telephone extension. But customers largely bought the systems for their then-new voice and management facilities. The systems needed secure electricity night and day (2 to 15
kilowatt The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after Jame ...
s).


Extension facilities

Facilities for the extensions were revolutionary at the time and particularly valued by organisations in financial and other industries with relatively highly-paid office-based employees: * Touch-tone telephones (then practically new to Europe) for both voice and data entry * Call rerouting from multiple extensions to answer points *
Camp on Last-call return, automatic recall, or (on PBX and centrex service) camp-on, is a telecommunication feature offered by telephony service providers to subscribers to provide the subscriber with the telephone number, and sometimes the time, of t ...
to a busy extension or external circuit with automatic call back * Short-code dialling to national and international numbers * Temporary call barring * Distinctive ring cadences (different cadences for internal and incoming external calls) * Dialled
paging In computer operating systems, memory 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 storag ...
* Group answering * Authorised user intrusion * Add-on third party *
Call pick-up Call pick-up is a feature used in a telephone system that allows one to answer someone else's telephone call. The feature is accessed by pressing a pre-programmed button (usually labelled "Pick-Up"), or by pressing a special sequence of buttons on ...
* Non-dialled connection (an off-hook extension automatically dials an extension).


Management facilities

Most management facilities were new to the PABX market: * IBM 3755 Operator Desk: optionally with braille-coded keys and audible alarms * Extension number and facility changes made from a central keyboard * Call cost recording * Classes of service for extensions * Traffic analysis * Night service: pre-night, standard, special-type-1, and special-type-2 night services.


Data facilities

The then-novel data facilities included: * Data collection available from every touch-tone extension to the switching system or through it to an IBM computer * IBM 3221 Numeric Multi-function Device: an extension-connected desktop terminal with a numeric keyboard and badge/card reader * IBM 3223 Entry/Exit Reporter: an extension-connected wall-mounted magnetic-card-reader terminal for attendance recording and controlled access to secure areas * Contact monitoring and operation. IBM’s customers for instance used the data functions for staff to report chargeable activity from their telephones.


Later additional facilities

Over time IBM introduced further functions: * Satellite operation (remote operator call handling) * The IBM Audio Distribution System (IBM 7770, based on an
IBM Series/1 The IBM Series/1 is a 16-bit minicomputer, introduced in 1976, that in many respects competed with other minicomputers of the time, such as the PDP-11 from Digital Equipment Corporation and similar offerings from Data General and HP. The S ...
computer) – then-novel centralised voice-message recording for up to three thousand 1750, 3750 and worldwide users; 100 hours of recorded messages; and optional connection to an IBM computer for notification on recipients' screens * Hotel functions such as automatic wake-up calls * Partitioning: multiple organisations using one system.


Networking

Widespread networks of systems became an important market for IBM. These multiple interconnected systems had central operating and control functions, tie-line busy back-up or rerouting via the public network, traffic saturation control, tie-line access restriction, network numbering up to 7 digits, remote paging, camping-on a remote extension, and adding a third party remotely.


Follow-on products

By about 1984 IBM could see that there would be few sales by about 1986 of the dated-technology 1750 and 3750 and that IBM's French development centre in La Gaude was not successfully developing a replacement product. So in 1984, IBM bought the American company ROLM that had more than 20,000 PABXs installed in the USA. IBM planned the ROLM system to be marketed in Europe as the IBM 8750, to replace the 1750 and 3750: despite much IBM expenditure, this did not happen, largely because of the difficulty of modifying the ROLM product for European conditions. IBM then unsuccessfully negotiated to sell Siemens PABXs, before stopping marketing all
PABX A business telephone system is a multiline telephone system typically used in business environments, encompassing systems ranging in technology from the key telephone system (KTS) to the private branch exchange (PBX). A business telephone syst ...
s. IBM continued to maintain 1750s and 3750s, before contracting others to maintain them into the 2000s — these were among those few IBM products to be still in use for nearly 40 years after their market introduction.


IBM 8750

IBM bought land in Wootton Bassett just west of Swindon in England to build a ROLM factory for Europe — the land was not used. In 1987 IBM started to market the ROLM-derived IBM 8750 Business Communications System in Austria, Belgium, France, Germany, Italy, Luxemburg, and the UK. Principally for homologation, a few had been installed in IBM locations, such as IBM Havant and IBM Portsmouth in England – however none were installed in customer locations. The 8750 had from 91 to 3000 telephone extensions; up to 1000 simultaneous conversations; a computer based on a
Motorola 68020 The Motorola 68020 ("''sixty-eight-oh-twenty''", "''sixty-eight-oh-two-oh''" or "''six-eight-oh-two-oh''") is a 32-bit microprocessor from Motorola, released in 1984. A lower-cost version was also made available, known as the 68EC020. In keepin ...
; up to 16 IBM 8755 Operator Consoles; a 30MB fixed disk; main/satellite working with 3750s and 1750s; digital trunks in Belgium, Italy and the UK; and used
ISDN Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network. Wor ...
and
Systems Network Architecture Systems Network Architecture (SNA) is IBM's proprietary networking architecture, created in 1974. It is a complete protocol stack for interconnecting computers and their resources. SNA describes formats and protocols but, in itself, is not a pi ...
(SNA) networks.IBM brochure G511-1025-0 dated 10/1987; System description GA19-5480 and 20 other manuals


References

{{reflist Telephone exchange equipment 1750, 2750 and 3750