|Properties||Fortran 66||Fortran 77||Fortran 90||Fortran 95|
|Fixed form||Fixed form||Fixed||Free||(Fixed)||Free|
|Whole Fortran 66||=||-2||-2||-2||-5||-5|
|Whole Fortran 77||-||=||=||=||-5||-5|
|Whole Fortran 90||-||-||=||=||-5||-5|
|Whole Fortran 95||-||-||-14||-14||=||=|
|Continuation line indicated in column 6|
on the next line
|Continuation line indicated with &|
at the end of the present line
|Blank line as comment||-||+||+||+||+||+|
|User-defined generic functions||-||-||+||+||+||+|
|Comment symbol||C||C *||C * !||!||C * !||!|
|Extension in Unix||.f||.f||.f||.f90||.f||.f90|
|Extension in DOS||.FOR||.FOR||.FOR||.F90||.FOR||.F90|
Above, for example, -2 in the position Whole Fortran 66 / Fortran 90 means that two properties have disappeared at the transition from Fortran 66 to Fortran 90. This applies to both fixed form and free form source code.
In the first four lines an equality sign = indicates that nothing has changed, a minus - that several properties are missing.
In the following seven lines a plus + indicates that the property is present, a minus - that it is absent.
Fixed form of the source code is discouraged in Fortran 95!
REAL*8 is an alternative to DOUBLE PRECISION, introduced by IBM and used also by Digital. Several variants exist.
As comment symbol the exclamation mark ! is recommended, it is valid also in several implementations of Fortran 77.
In UNIX there is no concept called extension, and the extensions are not specified in the Fortran standard, but in informal manufacturer standards.