Launched in 1981, Sir Clive Sinclair's ZX81 - successor to his ZX80 released the year before - was designed to be a low-cost introduction to home computing for the general public. It was a hugely successful machine, with over one and a half million 'official' units being sold; many more unauthorised 'clones' were also produced, particularly in Russia and other Eastern Bloc countries of the era. One could either purchase the machine...