The Free On-line Dictionary of Computing (30 December 2018):
A number representation scheme where a number,
F is represented by an integer I such that F=I*R^-P, where R is
the (assumed) radix of the representation and P is the (fixed)
number of digits after the radix point.
On computers with no floating-point unit, fixed-point
calculations are significantly faster than floating-point as
all the operations are basically integer operations.
Fixed-point representation also has the advantage of having
uniform density, i.e., the smallest resolvable difference of
the representation is R^-P throughout the representable range,
in contrast to floating-point representations.
For example, in PL/I, FIXED data has both a precision and
a scale-factor (P above). So a number declared as 'FIXED
DECIMAL(7,2)' has a precision of seven and a scale-factor of
two, indicating five integer and two fractional decimal
digits. The smallest difference between numbers will be 0.01.