Bell 101

The Bell 101 Data Set was the first commercial modem for computers, released by AT&T Corporation in 1958 for use by SAGE, and made commercially available in 1959, shortly after AT&T's Bell Labs announced their 110 baud modulation frequencies.^[1][2] The Bell 101 allowed digital data to be transmitted over regular unconditioned telephone lines at a speed of 110 bits per second.

The back of a Teletype Model 33 teleprinter with a Bell 101C Data Set in the pedestal, 1963.

The Bell 101 modem used audio frequency-shift keying to encode data. Different pairs of audio frequencies were used by each station:^[3]

• The originating station used a mark tone of 1,270 Hz and a space tone of 1,070 Hz.
• The answering station used a mark tone of 2,225 Hz and a space tone of 2,025 Hz.

Bell 101 modems are no longer in use and were quickly replaced by its successor the Bell 103 modem. SAGE modems were described by AT&T's Bell Labs as conforming to the Bell 101 data set standard.

See also

• List of interface bit rates
• Bell 202