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**Date Submitted:** 11/21/2012 04:33 AM

2.0 EVOLUTIONS AND TYPES OF COMPUTERS 2.1 Evolution of computers Evolution of computers can be traced as far back to around 5000 B.C. when human beings of those days were looking for an easy way of performing calculations. In this section we will briefly discuss some of the path-breaking inventions in the field of computing devices. These inversions lead to the generation of the diverse types of computers we see today.

2.1.1 Calculating Machines

Abacus It took over generations for early man to build mechanical devices for counting large numbers. The first calculating device called Abacus was developed by the Egyptian and Chinese people. The word Abacus means calculating board. It consisted of sticks in horizontal positions on which were inserted sets of pebbles. A modern form of Abacus is given in Fig. 2.1. It has a number of horizontal bars each having ten beads.

Horizontal bars represent units, tens, hundreds, etc.

Figure 2.1: The Abacus

Napier’s bones English mathematician John Napier built a mechanical device for the purpose of multiplication in 1617 A D. The device was known as Napier’s bones. Napier’s bone is a next calculating machine to Abacus.

Slide Rule English mathematician Edmund Gunter developed the slide rule. This machine could perform operations like addition, subtraction, multiplication, and division. It was widely used in Europe in 16th century. Computations by the slide rule were based on the principles of logarithms. Principally, a slide rule consists of two sliding graduated scales that slide on top of each other. Readings are taken when marks on the two scales coincides.

Figure 2.2: Slide Rule

Pascal's Adding and Subtractory Machine You might have heard the name of Blaise Pascal. He developed a machine at the age of 19 that could add and subtract known as Pascal's Adding and Subtractory Machine. The machine consisted of wheels, gears and cylinders.

Figure 2.3: Pascal's Adding and Subtractory Machine

Leibniz’s...