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The Processor!

© Ankan Brahmachari

Inside the Processor

The heart of the computer is the central processor unit (CPU). If you open it up, there is nothing much to see if you are looking for "moving parts". There are rows of printed circuit boards containing dozens of little black rectangles called chips or integrated circuits (IC). This truly is a marvelous device which first appeared a little over thirty years ago in calculators and watches. I can still recall my dad's digital watch, which he had to shake to read the time, but it was a wonderful device just the same.

The rectangles themselves are plastic casing surroundings thumbnail sized squares of an element called silicon. Through a very sophisticated process called micro lithography, electronic circuits are sketched directly on the surface of the silicon are scales smaller than a thousandth of your hair and even more. These circuits contain various components such as resistors, capacitors, transistors and "wires" or electrical pathways connecting them.

The transistors are the most important component of these circuits. It was invented in 1948; it soon found application in small radios and other devices. Its major function is to control electric currents. It is the presence of transistors that distinguishes electronic circuit from the common electrical ones.

The predecessor of the transistor was the valve or vacuum tube, which looked like a small light bulb. Your grandfather's radio set was full of valves, as was the first computer, the ENIAC, built in 1943. When individual transistors replaced valves, there was a ten -to twenty fold reduction in size in devices using them. With transistors now etched directly on silicon surfaces, there is a further hundred fold reduction in size. Miniaturization is a characteristic feature of modern electronics. The first chip of the early 70s had a few hundred transistors. Twenty years later, improved techniques have enabled over a million transistors to be crammed into a chip of the same size. In other words, the number of transistors on a chip has doubled approximately every 2 year.

The presence of so many transistors inside a computer doesn't make it a "super radio". This is because a computer is a device using digital electronics. The transistors on a chip are wired together in such a manner that they behave as switches - either they pass a tiny current or they do not. By contrast, a radio set uses analog circuits. It has to produce continuously varying audible sounds from the small signals picked up by its antenna. When you come right down to it, therefore, a computer does all the wonderful work by moving small currents around million or tiny circuits.