PL/I
PL/I is a third-generation ( 3GL ) programming language developed in the early 1960s as an alternative to assembler language (for low-level computer processing functions), COBOL (for large-scale business applications), and FORTRAN (for scientific and algorithmic applications). PL/I stands for "Programming Language 1". PL/I was an antecedent of the C programming language, which essentially replaced it as an all-purpose serious programming language.
PL/S , which IBM evolved from PL/I, was, until the advent of C , IBM's language of choice for its operating systems and application subsystems.