The earliest computing device undoubtedly consisted of the five fingers of each hand, and this is still the preferred device of every child who learns to count. Since there are ten discrete fingers (digits) available for counting, both digital computation and the decimal system have enjoyed a huge popularity throughout history. However, improvements were made to replace the digits of the hand by a more reliable ´ count-10´ device.
It probably did not take more than a few million years of human evolution before someone had the idea that pebbles could be used just as well as fingers to count things. Thus, ten pebbles or ten of anything were kept in a handy container to represent the numbers 1 to 10, instead of the ten fingers. The form the pebble container should take for handy calculations kept many of the best minds of the Stone Age busy for centuries. It was not till about five thousand years ago in the Tigris-Euphrates Valley (and as late as 460 BC in Egypt) that there arose the idea of arranging a clay board with a number of grooves into which the pebbles were placed. By sliding the pebbles along the grooves from one side of the board to the other, counting became almost ´ semi-automatic ´; even to the point allowing one hand to be kept free for other things. The grooved pebble container was too big a thing to be kept secret for long, and the processes of cultural diffusion (e.g. deported slaves) saw to it that it became known in China, Japan, and Rome. When the diversity of these races were confronted with this leap into the future, a flowering of ingenuity - a sort of minor renaissance - resulted, which swept the pebble computer to a high plateau of development. One group came up the idea of drilling holes in the pebbles and stringing the resulting beads in groups of ten of a frame of wire; another used reeds instead. In eihter case, the beads could be moved easily and rapidly along the wire or reeds, and a tremendous speed-up in calculations resulted. This device, is somewhat more sophisticated form, became known as the abacus in China.
The Chinese abacus is made of 13 columns with 2 beads on top (heaven) and 5 beads below (earth). The Japanese copied the Chinese abacus around the 17th century AD and adapted it to their more delicate way of thinking. It has 21 columns with 1 bead on top and 4 beads below. The abacus is still taught in the Far East as regular school training, and is used commonly in many places. In 1946 a contest between a Japanese abacist (Kiyoshu Matzukai) and an electronic computer was held for 2 days resulting in an unmistakable victory of the abacist. The third modern form of the abacus is Russian with 10 beads in 10 arched rows.
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"Electronic Computers Made Simple" by Henry Jakobowitz