The term artificial intelligence (AI) refers to the ability of a digital computer or computer-controlled robot to perform tasks commonly associated with intelligent beings. Since the mid-20th century, scientists have attempted to develop a system capable of carrying out tasks perceived as requiring human intelligence. Among the tasks that have been studied from this point of view are game playing, natural-language understanding, fault diagnosis, robotics, and supplying expert advice. Although computers can be programmed to perform these and other very complex tasks—and while advances continue to be made in computer processing speed and memory capacity—there are as yet no programs that can match human flexibility over wider domains or in tasks requiring much everyday knowledge.