Thursday, June 5, 2008

Rotary dial

The rotary dial is a device mounted on or in a telephone or switchboard that is designed to send interrupted electrical pulses, known as pulse dialing, corresponding to the number dialed. The early form of the rotary dial used lugs on a finger plate instead of holes. A patent was filed on August 20, 1896 by employees of Almon Strowger, namely, A. E. Keith and the brothers John and Charles Erickson. The Patent No. 597,062 was granted on January 11, 1898.

The modern version of the rotary dial with holes was first introduced in 1904 but only entered service in the Bell System in 1919. The device was phased out from the 1970s onwards with the onset of Touch Tone dialing, which uses a telephone keypad instead of a dial. Some telephone systems in the US no longer recognize rotary dialing by default, in which case it would have to be ordered from the telephone company as a special feature, to support older customer equipment.
Today the dial is a key pad or "dial pad", generally with 12 keys numbered 0-9, *, and # that perform an equivalent signalling function to that of a rotating disk dial.

In telephony, the word dialing (in present and past tense spelt with two Ls in British English and with one in American English) describes the process of the placement of a telephone call.

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