A 1G analog cellular radio derivate of the Advanced Mobile Phone Service (AMPS) technology, TACS was developed for use in the United Kingdom. TACS operates in the 900 MHz band and supports either 600 or 1,000 channels of 25 kHz, compared with the 666/832 channels of 30 kHz supported by AMPS.A number of variations were developed, including Narrowband TACS (NTACS), Extended TACS (ETACS), and Japanese Total Access Communications System (JTACS). TACS found acceptance in very few nations, largely has been replaced by GSM, and is considered obsolete in the United Kingdom. See also 1G, AMPS, analog, cellular radio, channel, ETACS, GSM, and NTACS.