Although early number systems were not positional, all of the number systems most commonly used today are positional systems: the value of a number in such a system is determined not just by the digits in the number but also by the position in the number of each of the digits. If a positional system has a fixed radix (or fixed base) R then each digit ai in any number
is an integer in the range 0 to (
R – 1) and the number is interpreted as
Since this is a polynomial in
R, such numbers are sometimes called
polynomial numbers. The decimal and binary systems are both fixed-radix systems, with a radix of 10 and 2, respectively.
Fractional values can also be represented in a fixed-radix system. Thus,
is interpreted as
In a
mixed-radix (or
mixed-base)
system, the digit
ai in any number
lies in the range 0 to
Ri, where
Ri is not the same for every
i. The number is then interpreted as
for example, 122 days 17 hours 35 minutes 22 seconds is equal to
seconds