What is a user interface?

User interface (or UI) is one of those jargon-y terms that you hear from computer salespeople and other techno-geeks but that you may have never heard defined. User interface refers to the parts of a computer and its software that you (the computer user) see, hear, touch, or talk to. It is the set of all the things that allow you and your computer to communicate with each other. For example, if you are reading this on a computer screen, then you're looking at part of a user interface right now. The screen is showing you these words, communicating a message to you.

Like any good communication channel, a user interface is a two-way street. You don't want to just see or hear whatever the computer puts in front of you, you also want to tell it what you'd like to do. For instance, to get to this Web page, you "asked" your computer to show you pages on a certain subject. You may have used a mouse to point and click on a button or word, or maybe you spoke instructions to the computer. However you express it, everything you tell the computer is input; what it conveys to you is output. The ways you can receive output and give input depend entirely on the user interface.

The best user interfaces are the ones you don't have to pay much attention to. They make sense to you and do what you expect them to. When an interface is easy to use, you can spend your time doing your work instead of looking everywhere for the right button or key to press. It's almost transparent--you can see right through the interface to your own work.

Interacting with computers    A discussion of input and output devices used to communicate with users and the controls used to set preferences and make choices.

UI evolution   The evolution of the user interface, from the command-line to objects that borrow from the real world.