The classical way to use a computer is through a command-line window,
often called a terminal. Using the keyboard, one writes commands that
the computer will understand and execute. Since graphical
user-interfaces (GUIs) are now the dominating way to use computers, many
people have never used or even seen a command-line interface. The
terminal has the obvious disadvantage that the user must remember a
large number of commands, while in a GUI system the available programs
and commands are typically visible as icons or in menus. However, if one
gets past the first threshold of memorizing a few commands, the terminal
is a very efficient way to use a computer.