A set of standards for facsimile (fax) machines published by the ITU-T in 1984 as T.6. Group IV machines are highly specialized and relatively expensive fax computer systems designed to make use of digital circuits to improve quality and improve transmission speed at rates up to 64 kbps. Group IV fax machines also are backward-compatible with Group III and can connect to analog circuits. See also facsimile, Group I, Group II, Group III, T.30, and T.6.