Generally, a computer is any device that can perform numerical calculations even an adding machine, an abacus, or a slide rule. Currently, however, the term usually refers to an electronic device that can use a list of instructions, called a program, to perform calculations or to store, manipulate, and retrieve information.
Today's computers are marvels of miniaturization. Machines that once weighed 30 tons and occupied warehouse-size rooms now may weigh as little as three pounds (1.4 kilograms) and can be carried in a suit pocket. The heart of today's computers are integrated circuits (ICs), sometimes called microchips, or simply chips. These tiny silicon wafers can contain millions of microscopic electronic components and are designed for many specific operations: some control an entire computer (CPU, or central processing unit, chips); some perform millions of mathematical operations per second (math coprocessors); others can store more than 16 million characters of information at one time (memory chips).
In 1953 there were only about 100 computers in use in the entire world. Today hundreds of millions of computers form the core of electronic products, and more than 110 million programmable computers are being used in homes, businesses, government offices, and universities for almost every conceivable purpose.
Computers come in many sizes and shapes. Special-purpose, or dedicated, computers are designed to perform specific tasks. Their operations are limited to the programs built into their microchips. These computers are the basis for electronic calculators and can be found in thousands of other electronic products, including digital watches (controlling timing, alarms, and displays), cameras (monitoring shutter speeds and aperture settings), and automobiles (controlling fuel injection, heating, and air conditioning and monitoring hundreds of electronic sensors).
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 data manipulating 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, can simultaneously accommodate scores of users, and can perform complex mathematical operations, they are the mainstay of industry, research, and university computing centers.
The speed and power of supercomputers, the fastest class of computer, are almost beyond human comprehension, and their capabilities are continually being improved. The most sophisticated of these machines can perform nearly 32 billion calculations per second, can store a billion characters in memory at one time, and can do in one hour what a desktop computer would take 40 years to do. Supercomputers attain these speeds through the use of several advanced engineering techniques. For example, critical circuitry is supercooled to nearly absolute zero so that electrons can move at the speed of light, and many processors are linked in such a way that they can all work on a single problem simultaneously. Because these computers can cost millions of dollars, they are used primarily by government agencies and large research centers.
Computer development is rapidly progressing at both the high and the low ends of the computing spectrum. On the high end, by linking together networks of several small computers and programming them to use a language called Linda, scientists have been able to outperform the supercomputer. This technology is called parallel processing and helps avoid hours of idle computer time. A goal of this technology is the creation of a machine that could perform a trillion calculations per second, a measure known as a teraflop. On the other end of the spectrum, companies like Apple and Compaq are developing small, handheld personal digital assistants (PDAs). The Apple Newton, for example, lets people use a pen to input handwritten information through a touch-sensitive screen and to send mail and faxes to other computers. Researchers are currently developing microchips called digital signal processors, or DSPs, to enable these PDAs to recognize and interpret human speech. This development, which will permit people in all professions to use a computer quickly and easily, promises to lead to a revolution in the way humans communicate and transfer information.