Though modems existed for teletype since the 1940s, these transmitted at speeds of about 150 bpi. To meet demands of the U.S. military, in 1958 researchers at Bell Labs developed an improved modem (modulator-demodulator), using amplitude magnification to provide a way to convert digital signals to analog signals and back for transmission at speeds up to 1600 bpi over analog telephone lines. The Bell 101 modem was first released by AT & T in 1958 for the SAGE system of large computers used by NORAD. It was released commercially in 1959. Bell 101 modems were the first commercial equipment to use the ASCII character encoding standard, which was called "four row", as opposed to the Baudot "three row" 6-bit/character code predominant from 1908–1962.