Total Access Communication System (TACS) is an analogue mobile communications system used in the U.K. and a number of other countries. TACS is a derivative of the Advanced Mobile Phone System (AMPS) developed by AT&T for the U.S.A. Its prime differences are the radio frequencies, the radio channel bandwidth and the data signalling rates. TACS was introduced in the U.K. in 1985. It's introduction was very succesfull. Over 25 other countries used TACS.
TACS is an analogue FM system operating in the 890-915 MHz / 935-960 MHz band; the band in which GSM was introduced later. The radio channel bandwidth was 25 kHz, offering 1000 duplex channels in the 900 MHz band. Because TACS used a reduced radio channel bandwidth compared to AMPS, which has a bandwidth of 30 kHz, the data signalling rate had to be reduced.
A modified version of TACS has been in use in Japan. The Japanese version was called JTACS. The main difference are another radio frequency band in which it operated.