In computing, start is a command of the IBM OS/2, Microsoft Windows and ReactOS command-line interpreter cmd.exe (and some versions of COMMAND.COM) to start programs or batch files or to open files or directories using the default program. start is not available as a standalone program. The underlying Win32 API is ShellExecute. The command is also one of the basic commands implemented in the Keyboard Monitor (KMON) of the DEC RT-11 operating system.The TOPS-10 and TOPS-20 operating systems also provide a start command. It is used to start a program in memory at a specified address.