Phoenix (computer) - Communications

Communications

The IBM-supplied Telecommunications Access Method (TCAM) and communications controller were replaced in 1975 by a system, called Parrot, that was created locally by the staff of the Computer Laboratory, comprising their own software and a PDP-11 complex. Their goal in doing so was to provide a better user interface than was available with a standard IBM system, alongside greater flexibility, reliability, and efficiency. They wanted to support 300 terminals. The initial system, supplied in 1972, comprised the PDP-11 emulating an IBM 2703 transmission control unit, which TCAM communicated with just as though it were a 2703. The PDP-11 was used instead of a bank of 2703s because for a projected 300 terminals a bank of 2703s was not scalable, too expensive, and inadequate for the Computing Service's needs, since it required paper tape readers and card punches as well. Even this solution proved to be unsatisfactory, and in 1975 TCAM was replaced by Parrot, with 200 terminals connected to the PDP-11, of which 80 could be simultaneously active. For full technical details of Parrot, see the technical report by Hazel and Stoneley.