 The success of the ZX81 led almost immediately to enthusiasts producing a huge variety of peripherals and software . Clive Sinclair was " amused and gratified " by the attention the machine received but made little effort to exploit the demand , effectively ceding a very lucrative market to third party suppliers , a decision that undoubtedly forfeited a lot of potential earnings . W.H. Smith , for instance , was able to exploit a peculiarity of the ZX81 ; owners found that technically obsolete low @-@ fidelity mono tape cassette recorders worked better as storage devices than higher @-@ quality music systems . Smith 's purchased cheap " shoebox " cassette recorders in the Far East and sold them with the W.H. Smiths logo as " data recorders " . Over 100 @,@ 000 were sold in 18 months . 
