 The ZX81 was launched on 5 March 1981 in two versions ( though with identical components ) – a pre @-@ assembled machine or a cheaper kit version , which the user could assemble himself . Both versions were manufactured in Dundee , Scotland by Timex Corporation at the company 's Dryburgh factory . Timex had not been an obvious choice of manufacturing subcontractor , as the company had little previous experience in assembling electronics . It was a well @-@ established manufacturer of mechanical watches but was facing a crisis at the beginning of the 1980s . Profits had dwindled to virtually zero as the market for mechanical watches stagnated in the face of competition from the digital and quartz watches . Recognising the trend , Timex 's director , Fred Olsen , determined that the company would diversify into other areas of business . 
