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In mathematical numeral systems, the radix or base is the number of unique digits, including zero, that a positional numeral system uses to represent numbers. For example, for the decimal system (the most common system in use today) the radix is ten, because it uses the ten digits from 0 through 9.
In any numeral system, the base is written as "10" in that base. In a base ten numeral system, "10" represents the number ten; in a base two system, "10" represents the number two.
Etymology
Radix is a Latin word for "root". Root can be considered a synonym for base in the arithmetical sense.
In numeral systems
In the system with radix 13, for example, a string of digits such as 398 denotes the decimal number . More generally, in a system with radix ( > 1), a string of digits denotes the decimal number .
Commonly used numeral systems include:
The decimal system, the most used system of numbers in the world, is used in arithmetic. Its ten digits are "0–9".The duodecimal (dozenal) system, which is base 12, is often used due to divisibility by 2, 3, 4 and 6. It was traditionally used as part of quantities expressed in dozens and grosses.The binary numeral system, used internally by nearly all computers, is base two. The two digits are "0" and "1", expressed from switches displaying OFF and ON respectively.The hexadecimal system, which is base 16, is often used in computing. The sixteen digits are "0–9" followed by "A–F".The octal system, which is base 8, is occasionally used in computing. The eight digits are "0–7".The sexagesimal system, base 60, originated in ancient Sumeria and passed to the Babylonians. It is still used as the basis of our modern circular coordinate system (degrees, minutes, and seconds) and time measuring (minutes and hours).Base 64 is also occasionally used in computing, using as digits "A–Z", "a–z", "0–9", plus two more characters, often "+" and "/".The octal, hexadecimal and base-64 systems are often used in computing because of their ease as shorthand for binary. For example, every hexadecimal digit has an equivalent 4 digit binary number.
Radices are usually natural numbers. However, other positional systems are possible, e.g. golden ratio base (whose radix is a non-integer algebraic number), and negative base (whose radix is negative).
