 A Direct Memory Access Director (DMAD) IOP allowed for a new type of I/O controller which had more freedom to access main memory, and allowed the design of more intelligent communications controllers.A SCSI IOP generated a SCSI bus for attaching more modern disks, and also included an integrated Interval Timer, system console controller, and Calendar Clock so that an additional Normal Interface IOP and separate controllers was not required to support just these functions.Users of GEC 4000 series systems included many British university physics and engineering departments, the central computing service of University College London (Euclid) and Keele University, the JANET academic/research network X.25 switching backbone, Rutherford-Appleton Laboratory, Daresbury Laboratory, Harwell Laboratory, NERC, Met Office, CERN, ICI, British Telecom, SIP (Italian telco), Plessey, British Steel Corporation and BHP Steel real-time control of rolling steel mills, British Rail and London Underground for real-time train scheduling, London Fire Brigade and Durham Fire Brigade command and control systems, Suffolk Constabulary, and most of the National Videotex systems in the world including the Prestel viewdata service.