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PBX switchboard, 1975. A telephone switchboard is a device used to connect circuits of telephones to establish telephone calls between users or other switchboards. The switchboard is an essential component of a manual telephone exchange, and is operated by switchboard operators who use electrical cords or switches to establish the connections.
In the early days of telephony, companies used manual telephone switchboards, and switchboard operators connected calls by inserting a pair of phone plugs into the appropriate jacks. They were gradually phased out and replaced by automated systems, first those allowing direct dialing within a local area, then for long-distance and international ...
Early manual switchboards required the operator to operate listening keys and ringing keys, but by the late 1910s and 1920s, advances in switchboard technology led to features which allowed the call to be automatically answered immediately as the operator inserted the answering cord, and ringing would automatically begin as soon as the operator ...
Their names are derived from the telephone plugs used for connecting telephone calls in manual switchboards. One side of the line is connected to the metal tip of the plug, and the second is connected to a metal ring behind the tip, separated and insulated from the tip by a non-conducting material. When inserted into a jack, the plug's tip ...
Various methods were used to convert these to dialable numbers as dial systems replaced manual switchboards; many moderately-large cities used a 2L-4N format where "ADelaide 1234" would be dialled as AD-1234 (23-1234, a six-digit local call). The four largest cities (New York, Chicago, Philadelphia, and Boston) used seven digits.
The term PBX originated when switchboard operators managed company switchboards manually using cord circuits. As automated electromechanical switches and later electronic switching systems gradually replaced the manual systems, the terms private automatic branch exchange (PABX) and private manual branch exchange (PMBX) differentiated them.
EMS-1 (The ITEC Electronic Modular Switch is an electronic direct control switching system. The modules are combined to form a complete switch or any of the modules can be added to your present Step-by-Step Systems.) EMS-2 (The EMS-2 RURAL SWITCH is a stored program control analog switch designed to be cost-effective in small exchanges.
The GPO could only do this via PMBXs (manual switchboards), ranging from the two to five line cordless boards, via the 25 and 50 line plug and cord boards to the mighty PMBX 1A, which, with its modular construction, could be any size a large company might require.
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