A system program that accepts instructions from a command line and executes them. For example, COMMAND.COM was the command processor for the 16-bit DOS operating system. It was replaced with CMD.EXE, the 32-bit Windows command processor, which added support for file names longer than eight characters (see 8.3 names). In Unix/Linux, command processors are called "shells" (see bash shell, C shell and Bourne shell). See cmd abc's and command line.