General-purpose computers, such as personal computers and business computers, are much more versatile because they can accept new sets of instructions. Each new set of instructions, or program,enables the same computer to perform a different type of operation. For example, one program lets the computer act like a word processor, another lets it manage inventories, and yet another transforms it into a video game. Although some general-purpose computers are as small as pocket radios, the smallest class of fully functional, self-contained computers is the class called notebook computers. These usually consist of a CPU, data-storage devices called disk drives, a liquid-crystal display (LCD), and a full-size keyboard--all housed in a single unit small enough to fit into a briefcase. Today's desktop personal computers, or PCs, are many times more powerful than the huge, million-dollar business computers of the 1960s and 1970s. Most PCs can perform from 16 to 66 million operations per second, and some can even perform more than 100 million. These computers are used not only for household management and personal entertainment, but also for most of the automated tasks required by small businesses, including word processing, generating mailing lists, tracking inventory, and calculating accounting information. Minicomputers are fast computers that have greater datamanipulating capabilities than personal computers and can be used simultaneously by many people. These machines are primarily used by larger businesses to handle extensive accounting, billing, and inventory records. Mainframes are large, extremely fast, multi-user computers that often contain complex arrays of processors, each designed to perform a specific function. Because they can handle huge databases, cansimultaneously accommodate scores of users, and can perform complex mathematical operations, they are the mainstay of industry, research, and university computing centers. The ...
