The outer layer of an operating system, otherwise known as the user interface. The term originally referred to the software that processed the commands typed into the Unix operating system. For example, the Bourne shell was the original Unix command line processor, and C shell and Korn shell were developed later. The default command line interface in DOS was provided by the COMMAND.COM module, which, starting with Windows 95 was superseded by CMD.EXE. See
command line and
user interface.
Later, the term was applied to graphical user interfaces (GUIs). For example, the default shell in Windows is Explorer, which provides the Start menu, taskbar and desktop, but third-party choices are also available (see
skin). DOS also had an alternative to the command line (see
DOS Shell). See
Explorer,
PowerShell,
Bourne shell,
C shell and
Korn shell.