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 other than what Clarke described as "a few remarkably poor programs on cassette" 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.