plication, division, and other functions. In a typical electronic analog 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. b) What are digital computers and how do they work? Everything that a digital computer does is based on one operation: the ability to determine if a switch, or "gate," is open or closed. That is, the computer can recognise 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 10 MHz-a fairly representative speed for a microcomputer-is capable of executing 10 million discrete operations each second. Business microcomputers can perform 15 to 40 million operations per second, and 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 symbolise one operation or number, and OFF would symbolise another. By checking groups of switches linked as a unit, however, the computer increases the number of operations it can recognise at each cycle. For example, a computer that checks two switches at one time can represent four numbers (0 to 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). II. WHERE IT ALL BEGAN a) The Mother of all Calculators The first adding machine, a precursor of the dig...
