Late 1970s - Present: Fourth Generation Computers Following the invention of the first integrated circuits always more and more components could be fitted onto one chip. LSI (Large Scale Integration) was followed by VLSI (Very Large Scale Integration) and ULSI (Ultra-Large Scale Integration), which increased the number of components squeezed onto one chip into the millions and helped diminish the size as well as the price of computers. The new chips took the idea of the integrated circuit one step further as they allowed to manufacture one microprocessor which could then be programmed to meet any number of demands. Also, ensuing the introduction of the minicomputer in the mid 1970s by the early 1980s a market for personal computers (PC) was established. As computers had become easier to use and cheaper they were no longer mainly utilized in offices and manufacturing, but also by the average consumer. Therefore the number of personal computers in use more than doubled from 2 million in 1981 to 5.5 million in 1982. Ten years later, 65 million PCs were being used. Further developments included the creation of mobile computers (laptops and palmtops) and especially networking technology. While mainframes shared time with many terminals for many applications, networking allowed individual computers to form electronic co-operations. LANs (Local Area Network) permitted computers to share memory space, information, software and communicate with each other. Although already LANs could reach enormous proportions with the invention of the Internet an information and communication-network on a global basis was established for the first time.

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Expert system Expert systems are advanced computer programs that mimic the knowledge and reasoning capabilities of an expert in a particular discipline. Their creators strive to clone the expertise of one or several human specialists to develop a tool that can be used by the layman to solve difficult or ambiguous problems. Expert systems differ from conventional computer programs as they combine facts with rules that state relations between the facts to achieve a crude form of reasoning analogous to artificial intelligence. The three main elements of expert systems are: (1) an interface which allows interaction between the system and the user, (2) a database (also called the knowledge base) which consists of axioms and rules, and (3) the inference engine, a computer program that executes the inference-making process. The disadvantage of rule-based expert systems is that they cannot handle unanticipated events, as every condition that may be encountered must be described by a rule. They also remain limited to narrow problem domains such as troubleshooting malfunctioning equipment or medical image interpretation, but still have the advantage of being much lower in costs compared with paying an expert or a team of specialists.

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