in order to proactively manage the potentially large numbers of user connections to prestel computers, special monitoring equipment was developed by post office research and development engineers. this was known by the acronym vampire, short for "viewdata access monitor and priority incident reporting equipment" – a title which more or less describes its function. the device used private circuits to connect modem ports on each computer or remote irc multiplexor node, with a display on a television screen prestel prestel at the regional centre responsible for the administration of irc. the vampire screen consisted of a matrix of small squares, so arranged that all ports for a single irc computer could be displayed on a single television with each square representing the state of a port simply by means of the colour. free ports were shown as green, occupied ports as yellow, incoming calls as pale blue and faulty ports as red, such that the state of a whole prestel machine or concentrator node could be determined at a glance.