Except as noted here, the Fortran 95 standard is an upward-compatible extension to the preceding Fortran International Standard, ISO/IEC 1539-1:1991, informally referred to as Fortran 90. A standard conforming Fortran 90 program that does not use any of the features deleted from the Fortran 95 standard, is a standard conforming Fortran 95 program, as well. The Fortran 90 features that have been deleted from the Fortran 95 standard are the following:
Fortran 95 allows a processor to distinguish between a positive and a negative real zero, whereas Fortran 90 did not. Fortran 95 changes the behavior of the SIGN intrinsic function when the second argument is negative real zero.
More intrinsic functions appear in the Fortran 95 standard than in the Fortran 90 standard. Therefore, a program that conforms to the Fortran 90 standard may have a different interpretation under the Fortran 95 standard. The different interpretation of the program in Fortran 95 will only occur if the program invokes a procedure that has the same name as one of the new standard intrinsic procedures, unless that procedure is specified in an EXTERNAL statement or with an interface body.