User Interface

The user interface is the part of the operating system you deal with directly. It lets you control the computer by taking your input, such as a tap, a click or a typed command, and displaying output back to you on the screen. Without it the operating system would still be running, but you would have no way to tell it what you wanted.

Input and output working together

An interface pairs what you do with what you see. When you tap a button, the operating system receives that input, works out which option you chose, and changes the display so you can see the result. That loop is what makes a computer usable: input tells the operating system what you want, and output shows you what happened.

For example, at a cinema ticket machine you tap the name of the film you want, which is the input, and the screen shows the seats that are still free, which is the output. You then tap a seat and the screen shows the ticket price. Each tap changes what is displayed, so you always know what to do next.

Not always graphical

Many interfaces are graphical: they show windows, icons and menus, so the choices are visible and you can explore without learning command names. Others are command-line interfaces, where you type a line of text and press Enter; you must know the exact command, but it is still a user interface taking input and giving output. Whoever sets up the computer chooses the type, and the interface is only one of the operating system's jobs.