Human-computer interaction (HCI) is the study of how people use computers, with the aim of making them easier to use. It has grown in importance as a topic as computers have become less expensive and, thus, are now used by many more people. In the early years of computers (the 1950s to the 1970s), computers were expensive and generally only used by skilled people, often computer scientists. The aim in writing programs was to squeeze the most power from a very limited memory and processing speed. It made sense to pay little attention to the usability of the system when the computer cost millions of dollars and could barely perform the task required. Since the 1980s, as computers have become less expensive and particularly as they have become more widespread, the problems of usability have become more intense. Systems developers can no longer assume that the...