Dynamic access to the numerical properties of the implementation can enable the development of portable numerically robust software. Fortran 90 provides such access through a combination of a model of the methods for approximating real values and a set of corresponding intrinsic functions for extracting model values. These intrinsic functions, of which there are a total of 16, are called the environmental inquiry (nine) and numeric manipulation (seven) intrinsic functions.
Each kind of real number is modeled by
The principal characteristics of a given real kind are its values for and and its range for .
IEEE arithmetic is based upon a binary (=2) representation in which =24 (single precision), =56 (double precision), and ; IEEE uses what would be an exponent of to represent zero and NaNs (illegal or out-of-range values). A nonbinary example is that of IBM 370 real arithmetic, in which =16, =6 (single precision), =14 (double precision), and -127e127. In most implementations the main difference in the representation of different real kinds is the value of , though it is possible (and occasionally happens) for the value of or the range of to vary between kinds.