Command history is a feature in many operating system shells, computer algebra programs, and other software that allows the user to recall, edit and rerun previous commands. Command line history was added to Unix in Bill Joy's C shell of 1978; Joy took inspiration from an earlier implementation in Interlisp. It quickly became popular because it made the C shell fast and easy to use. History has since become a standard feature in other shells, including ksh, Bash and Microsoft's cmd.exe. History addressed two important scenarios: