 Reviews of the ZX81 highlighted the great value for money offered by the machine but noted its technical shortcomings . As Tim Hartnell put it in Your Computer , " the ZX81 is both a delight and a disappointment " . He applauded the improvements that had been made over the ZX80 , such as a much better manual , display and string handling , and called the ZX81 " a very good first computer " that " will open the world of computing to many who would be denied access to it by cost . " However , the built @-@ in memory was so small that use of a memory expansion pack was " mandatory for any worthwhile use " . He also found the ZX81 to be alarmingly unreliable , having to have his first two test machines replaced before getting one that worked properly . 
