Fortran 90 included a large number of features that allowed programmers to specify operations on a whole array at once.
High Performance Fortran was an attempt at an extension to Fortran 90 which would allow efficient and full use of computers belonging to a number of parallel architectures.
Most, but not all, of the statements added to Fortran by HPF appeared in comments prefixed with
!HPF$
and this idea is also used elsewhere. A version of Fortran 2003 for Cray supercomputers used !DIR$ for some directives, and !CSD$ for others. As for !HPF$, the features of High Performance Fortran were made part of the official Fortran standard with Fortran 95.