Term: shell

Shell refers to a computer operating system’s primary user interface.

Shell is actually a very old term, pre-dating even MS-DOS itself. Originally, it referred to the program that accepted typed-in commands, interpreted them, and ran corresponding programs to carry out the desired actions. In Windows, the program “cmd.exe” can be considered a shell, operating in much the same way. The “Windows PowerShell” is essentially an enhanced version, and a very similar program.

The concept of multiple, different shells is also not new. Early versions of Unix included a standard shell, “sh”, but was soon augmented with a variant known as “csh”, or c-shell, whose command syntax was designed to more closely resemble the “C” programming language. In today’s modern Linux distributions, sh and csh remain, and a third option, “bash”, is also present.

With the advent of graphical operating systems, the term shell has been somewhat deprecated. It can still be used to refer to the program that displays and controls the operating system’s primary user interface. In Windows, that program is “explorer.exe”, which, when initially run, displays the desktop, Task Bar, Start menu, and more. (It’s only on subsequent runs that the same explorer.exe acts as a stand-alone file-management program.)