TheHindu-Arabic system

Several different claims, each having a certain amount of justification, have been made with respect to the origin of modern Western numerals, commonly spoken of asArabic but preferably as Hindu-Arabic. These include the assertion that the origin is to be found among the Arabs, Persians, Egyptians, and Hindus. It is not improbable that the intercourse among traders served to carry such symbols from country to country, so that modern Western numerals may be a conglomeration from different sources. However, as far as is known, the country that first used the largest number of these numeral forms isIndia. The 1, 4, and 6 are found in theAshokainscriptions (3rd centurybce); the 2, 4, 6, 7, and 9 appear in theNana Ghat inscriptions about a century later; and the 2, 3, 4, 5, 6, 7, and 9 in the Nasik caves of the 1st or 2nd centuryce—all in forms that have considerable resemblance to today’s, 2 and 3 being well-recognized cursivederivations from the ancient = and ≡. None of these early Indian inscriptions gives evidence of place value or of a zero that would make modern place value possible. Hindu literature gives evidence that the zero may have been known earlier, but there is no inscription with such asymbol before the 9th century.

The first definite external reference to the Hindu numerals is a note bySeverus Sebokht, a bishop who lived in Mesopotamia about 650. Since he speaks of “nine signs,” the zero seems to have been unknown to him. By the close of the 8th century, however, some astronomical tables of India are said to have been translated into Arabic atBaghdad, and in any case the numeral became known to Arabian scholars about this time. About 825 the mathematicianal-Khwārizmī wrote a small book on the subject, and this was translated into Latin byAdelard of Bath (c. 1120) under the title ofLiber algorismi de numero Indorum. The earliest European manuscript known to contain Hindu numerals was written inSpain in 976.

The advantages enjoyed by the perfected positional system are so numerous and somanifest that the Hindu-Arabic numerals and thebase 10 have been adopted almost everywhere. These might be said to be the nearest approach to auniversal human language yet devised; they are found in Chinese, Japanese, and Russian scientific journals and in every Western language. (However,see thetable for some other modern numeral systems.)

Thebinary system

There is one island, however, in which the familiardecimal system is no longer supreme: the electroniccomputer. Here the binary positional system has been found to have great advantages over the decimal. In the binary system, in which the base is 2, there are just two digits, 0 and 1; the number two must be represented here as 10, since it plays the same role as does ten in the decimal system. The first few binary numbers are displayed in thetable.

A binary number is generally much longer than its corresponding decimal number; for example, 256,058 has the binary representation 111 11010 00001 11010. The reason for the greater length of the binary number is that a binary digit distinguishes between only two possibilities, 0 or 1, whereas a decimal digit distinguishes among 10 possibilities; in other words, a binary digit carries less information than a decimal digit. Because of this, its name has been shortened tobit; a bit of information is thus transmitted whenever one of twoalternatives is realized in the machine. It is of course much easier to construct a machine to distinguish between two possibilities than among 10, and this is another advantage for the base 2; but a more important point is that bits serve simultaneously to carry numerical information and thelogic of the problem. That is, thedichotomies of yes and no, and of true and false, are preserved in the machine in the same way as 1 and 0, so in the end everything reduces to a sequence of those two characters.