Radix
Number of digits of a numeral system
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Through Positional notation, Numerical digit and Decimal
In any standard positional numeral system, a number is conventionally written as (x)y with x as the string of digits and y as its base. For base ten, the subscript is usually assumed and omitted (together with the enclosing parentheses), as it is the most common way to express value. For example, (100)10 is equivalent to 100 (the decimal system is implied in the latter) and represents the number one hundred, while (100)2 (in the binary system with base 2) represents the number four.
Electronic computers process and store information in the simplest way, as bits of binary code, which have a radix of 2.
Etymology
Radix is a Latin word for "root". Root can be considered a synonym for base, in the arithmetical sense.
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In numeral systems
Generally, in a system with radix b (b > 1), a string of digits d1 ... dn denotes the number d1bn−1 + d2bn−2 + ... + dnb0, where 0 ≤ di < b. In contrast to decimal, or radix 10, which has a ones' place, tens' place, hundreds' place, and so on, radix b would have a ones' place, then a b1s' place, a b2s' place, etc.
For example, if b = 12, a string of digits such as 59A (where the letter "A" represents the value of ten) would represent the value 5 × 122 + 9 × 121 + 10 × 120 = 838 in base 10.
Commonly used numeral systems include:
The octal and hexadecimal systems are often used in computing because of their ease as shorthand for binary. Every hexadecimal digit corresponds to a sequence of four binary digits, since sixteen is the fourth power of two; for example, hexadecimal 7816 is binary 11110002. Similarly, every octal digit corresponds to a unique sequence of three binary digits, since eight is the cube of two.
This representation is unique. Let b be a positive integer greater than 1. Then every positive integer a can be expressed uniquely in the form
where m is a nonnegative integer and the r's are integers such that
- 0 < rm < b and 0 ≤ ri < b for i = 0, 1, ... , m − 1.
Radices are usually natural numbers. However, other positional systems are possible, for example, golden ratio base (whose radix is a non-integer algebraic number), and negative base (whose radix is negative). A negative base allows the representation of negative numbers without the use of a minus sign. For example, let b = −10. Then a string of digits such as 19 denotes the (decimal) number 1 × (−10)1 + 9 × (−10)0 = −1.
Table of bases
Different bases are especially used in connection with computers. The commonly used bases are 10 (decimal), 2 (binary), 8 (octal), and 16 (hexadecimal). A byte with 8 bits can represent values from 0 to 255, often expressed with leading zeros in base 2, 8 or 16 to give the same length.
The first row in the tables is the base written in decimal.