Double Precision Type

  Double precision is an alternative floating-point type. The Fortran Standard only specifies that it should have greater precision than the real type but in practice, since the double precision storage unit is twice the size, it is safe to assume that the precision is at least doubled. The number range may, however, be the same as that for real type.

Although double precision values occupy twice as much memory as real (or integer) values, computations on them do not necessarily take twice as long.