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.