Few foresaw the rate of progress in information technology (IT) and the IT-producing industries over the last few decades—a brief period in which computing went from infancy to ubiquity. Digital technologies have become plentiful, inexpensive, and powerful. Through successive waves, computing advanced from stand-alone systems to batch processing, from batch processing to time-sharing, from time-sharing to personal computers, and now from personal computers to information appliances connected to the Internet. Each of these transitions enabled computing to reach an ever-widening circle of users. Microprocessors are now in machines everywhere, from supercomputers to servers, to very powerful desktop and portable computers, to consumer devices and specialized equipment of all kinds. They are embedded in automobiles, aircraft, and telephones, controlling such functions as antilock brakes, automated landing systems, and cellular call processing.

While small or everyday systems capture the popular imagination, large systems power many sophisticated applications. When characterizing IT systems, large can refer to the kind of problem to be solved, and so-called high-performance systems handle complex applications with large numbers of computations or store huge amounts of information. Large can also refer to the number of connections among devices and smaller systems, and thanks to the Internet, computer-based networking is increasingly large-scale, integrating products and applications from dif-