People need to represent real numbers in computers. Numbers which are not integers, i.e. contain fractional parts, as well as extremely large and extremely small numbers are needed by scientific and business applications, and even by people who just want to keep track of their money or balance their checkbook or convert from metric to English measurements. Floating point numbers are the computer entities which satisfy these needs and approximate real numbers.

Scientists needed to represent very large and very small numbers long before computers came along. For example, the mass of the hydrogen atom is about 1.67339×10^-24 grams. This number would be 0.00000000000000000000000167339 if written out as a pure fraction, which is ridiculously clumsy to write, read, and work with.