Sign-value notation

From Wikipedia, the free encyclopedia

1 In Computers
2 In Ancient Number Systems
3 References
4 External links

[edit] In Computers

Sign-value notation (sign-magnitude notation) in computers is the use of the high-order bit (left end) of a binary word to represent the numeric sign: 0 for + and 1 for - followed by a binary number that is an absolute magnitude or a two's complement of an absolute magnitude. For example, 01001 means plus 9. In 2's complement: 11101 means minus 3 and 10111 means minus 9. See also Signed number representations

[edit] In Ancient Number Systems

Sign-value notation represents numbers by a series of numeric signs that added together equal the number represented. In Roman numerals for example, X means ten and L means fifty. Hence LXXX means eighty (50 + 10 + 10 + 10). There is no need for zero in sign-value notation. Sign-value notation was the pre-historic way of writing numbers and only gradually evolved into place-value notation, also known as positional notation.

When pre-historic people wanted to write "two sheep" in clay, they could inscribe in clay a picture of two sheep. But this would be impractical when they wanted to write "twenty sheep". In Mesopotamia they used small clay tokens to represent a number of a specific commodity, and strung the tokens like beads on a string. There was a token for one sheep and a token for ten sheep, and a different token for ten goats, etc. To insure that nobody could alter the number and type of tokens, they invented a clay envelope shaped like a hollow ball into which the tokens on a string were placed. If anybody contested the number, they could break open the clay envelope and do a recount. To avoid unnecessary damage to the record, they pressed archaic number signs on the outside of the envelope before it was baked, each sign similar in shape to the tokens they represented. Since there was seldom any need to break open the envelope, the signs on the outside became the first written language for writing numbers.