by september 1980, there were five irc machines in london plus pairs of machines at birmingham, nottingham, edinburgh, glasgow, manchester, liverpool and belfast offering a total of 914 user ports. further irc's were planned at luton, reading, sevenoaks, brighton, leeds, newcastle, cardiff, bristol, bournemouth, chelmsford and norwich by the end of 1980. in some of these locations where there was insufficient prestel traffic to warrant siting an irc computer, the plans were to site multiplex equipment in a suitable exchange building from where connections were made over x25 to the nearest proper irc. as at the end of 1980, there was actually a total of 1500 live computer ports available and by july 1981, the number of irc computers has been expended to 18, increasing the coverage of the telephone subscriber population from 30% to 62%.