IBM 270x
270x is a generic name for a family of IBM non-programmable communications controllers used with System/360 and System/370 computers. The family consisted of the following devices: The 2701 and 2702 were announced simultaneously with System/360 in 1964, the 2703 was announced a year later. The 270x series was superseded by the IBM 3704 and 3705 communications controllers in 1972. 2701. The 2701 supported up to four start-stop or synchronous communications lines. It had two multiplexor channel interfaces for connection to one or two host computers. The synchronous adapter originally supported the "Synchronous Transmit-Receive (STR)" protocol , and later "Binary Synchronous Communications (BISYNC)" when it was introduced in 1967, in half duplex mode at speeds of up to 40,800 bits per second (bit/s). The 2701 could also have "data acquisition and control adapters" for direct control of external equipment. Initially the 2701 supported the following devices: Later the IBM 2740 and IBM 2741 Communication Terminals, and the IBM 2260/2848 were added. 2702. The 2702 could accommodate up to 31 communication lines, but at a slower speed than the 2701. The System/360 Configurator indicates that in the 2702 supported start-stop lines only. Initially the 2702 supported  the following terminals: Later the IBM 2740 and IBM 2741 Communication Terminals, the IBM 1032 Digital Time Unit, and a second channel interface were added. 2703. The 2703 supported up to 176 half-duplex start-stop or Binary Synchronous communication lines. The maximum speed of one line was 2400 bit/s but the total aggregate line speed was limited. By 1970 the maximum line speed had been raised to 4800 bit/s. The 2703 attached to a single multiplexer channel; each communication line occupied a subchannel. It had a four or eight byte buffer per line to reduce data transfer  to and from the host computer. The IBM 2712 Remote Multiplexer allowed up to fourteen slow speed devices to be multiplexed over one high speed line to a 2703. As of 1967 the 2703 supported the following devices: Clones. Many companies produced clones of 270x controllers, such as the Memorex 1270, introduced in 1970, and devices from NCR-Comten.