 Perhaps the most commercially successful implementation aside from IBM's was Digital Equipment's 1988 release of the ANSI PL/I 1987 subset.The implementation is "a strict superset of the ANSI X3.4-1981 PL/I General Purpose Subset and provides most of the features of the new ANSI X3.74-1987 PL/I General Purpose Subset".The front end was designed by Robert Freiburghouse, and the code generator was implemented by Dave Cutler, who managed the design and implementation of VAX/VMS.