In a typical electronic analogue computer, the inputs are converted into voltages that may be added or multiplied using specially designed circuit elements. The answers are continuously generated for display or for conversion to another desired form.

Digital Computers

Everything that a digital computer does is based on one operation: the ability to determine whether a switch, or "gate", is open or closed. That is, the computer can recognize only two states in any of its microscopic circuits: on or off, high voltage or low voltage, or-in the case of numbers-0 or 1. The speed at which the computer performs this simple act, however, is what makes it a marvel of modern technology. Computer speeds are measured in megahertz, or millions of cycles per second. A computer with a "clock speed" of 100 MHz-a fairly representative speed for a microcomputer-is capable of executing 100 million discrete operations each second. Supercomputers used in research and defence applications attain speeds of billions of cycles per second.

Digital computer speed and calculating power are further enhanced by the amount of data handled during each cycle. If a computer checks only one switch at a time, that switch can represent only two commands or numbers; thus ON would symbolize one operation or number, and OFF would symbolize another. By checking groups of switches linked as a unit, however, the computer increases the number of operations it can recognize at each cycle. For example, a computer that checks two switches at one time can represent four numbers (0-3) or can execute one of four instructions at each cycle, one for each of the following switch patterns: OFF-OFF (0); OFF-ON (1); ON-OFF (2); or ON-ON (3).