 The British chain stores Boots , John Menzies and Currys began selling the ZX81 as soon as Smith 's exclusive distribution deal expired and a number of companies secured overseas distribution rights for the ZX81 , which was being sold in 18 countries by March 1982 . Sinclair launched the ZX81 in the United States in November 1981 at a price of $ 149 @.@ 95 assembled and $ 99 @.@ 95 in kit form , initially selling directly to the American market by mail order . To be useful the computer needed an extra 16KB RAM pack which cost $ 49 @.@ 95 . Sales reached 15 @,@ 000 a month by January 1982 , while American Express sold thousands more to its own customers . In February 1982 Timex obtained a licence from Sinclair to sell the ZX81 directly through thousands of retail outlets in the US , paying Sinclair Research a 5 per cent royalty on all Sinclair hardware and software sold by Timex . The company was later to produce its own licensed clones and variants of the ZX81 . By August 1982 Sinclair had lowered the American mail @-@ order price of the assembled ZX81 to $ 99 @.@ 95 and kit to $ 79 @.@ 95 , and its advertisements stated that " more than 10 @,@ 000 are sold every week " . In December 1981 Mitsui obtained rights to distribute the ZX81 in Japan , selling it by mail order for ¥ 38 @,@ 700 ( equivalent to £ 83 in 1982 prices ) , and had sold 5 @,@ 000 units by July 1982 . The Japanese market 's favourable reaction to the ZX81 led Mitsui to begin selling the ZX81 over the counter in large bookshops from September 1982 , with annual sales of 20 @,@ 000 units predicted . In the Netherlands , the regular Sinclair ZX81 was for sale as well as a Bang & Olufsen branded version called Beocomp . 
