User Interfaces

The user interface describes how a user and computer interact with each other. This interaction is typically achieved via hardware devices such as the keyboard, the monitor and (if present) the mouse. In order to instruct a computer to perform a task, a user may type a command on the keyboard or may make a selection from a menu using the mouse. To convey information to the user, the computer may simply display text on the monitor screen, or perhaps display an image or play a sound etc.

Let's consider a few examples of different user interfaces in use today. On the one hand there is the traditional command line style interface, where a user communicates with the computer by typing commands on the keyboard and reading text on the screen. Examples of this type of user interface are the command line interpreter, or shell, on UNIX systems as shown in figure 1 and similarly the DOS prompt on PCs. With this kind of user interface, the user needs a good knowledge of the available commands, before using the computer effectively, and often error messages from the computer are rather unhelpful to the novice user. Such user interfaces, often derided as user-unfriendly, evolved at a time when computer power was poor, hardware was not so readily available and access to the computer was via terminals which could really do little more than read and display characters.

 
Figure 1: The UNIX C-Shell command line style user interface

On the other hand, there is the more recent user-friendly user interface where, using the mouse, commands can be selected from menus and buttons etc. displayed on the screen. With this type of user interface it is not necessary to be fluent with a vocabulary of commands, in order to use the computer. Examples of this type of user interface can be found on the Apple Macintosh as shown in figure 2, Microsoft Windows for PCs and most workstations. This kind of user interface is often known as a graphical user interface (GUI). They evolved at a time when computer hardware was becoming more sophisticated, more powerful and cheaper. The idea of typing commands on a character based terminal to access a shared computer is now being replaced by a computer on the desk, with a bitmapped display for images, a mouse, as well as a keyboard, for input, plus network access to a multitude of services.

 
Figure 2: The Macintosh graphical user interface