The number of different numbers is specified by the used number system:
- In the most common decimal system there are ten numbers, i.e. the numbers 0 to 9, from which each number is compound.
- In the electronic data processinguses one, predominantly internally, the binary system with the two numbers 0 and 1. A binary (more =zweiwertiger) condition is used, each individual place of a number represents a bit in such a way specified .
- The hexadecimal number system (sextodecimal number system) uses additionally to thatNumbers 0 to 9 also still the letters A to F (often also small written). This alphanumeric mixing system with its sixteen numbers is, since center of the 1950er years, the standard representation for hexadecimal numbers. There this number system however in program codes not(„af123 “can describe the number of af123 or a variable with name af123), needs it is unambiguous Prä or Suffixe always clarifying (e.g. Prefix 0x). For some years a suggestion, hexadecimal numbers exists with new, unambiguous, so-called generally omni litteralen (i.e. onlyTo represent letter) numbers. (c.f. Hexadecimal in hexadecimals). The hexadecimal number system is gladly used in computer science, because it illustrates for each number accurately 4 bits and thus is related to the binary system.
- With BCD - Numbers has one a system of the computer engineering, thatwith 16-wertigen actually uses groups of only 10 values. It concerns thus a decimal system, which was adapted ago however to the binary system by use of hexadecimal well-known place arrangement.
- In the computer engineering still the octal system is as Exot, which is formed on the basis of the numbers 0 to 7.
- The Indians of South America did not use number systems for the basis 4, 8 or 16, since they counted on hands and feet, however the thumbs thereby to include wanted.
The terms number and number in the German language frequently are falsely synonymously used. For example in the term dark number, which is actually a number, thus mathematically correctly actually dark number are called would have. The correct use: The number of 23 consists of the numbers 2 and3 and not from the numbers 2 and 3. This is comparable for the formation rule of the writing: Words consist of letters, which also type characters are called.
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