Early History
In the 1950s and early 1960s business and scientific users programmed for different computer hardware using different programming languages. Business users were moving from Autocoders via COMTRAN to COBOL, while scientific users programmed in General Interpretive Programme (GIP), Fortran, ALGOL, GEORGE, and others. The IBM System/360 (announced in 1964 but not delivered until 1966) was designed as a common machine architecture for both groups of users, superseding all existing IBM architectures. Similarly, IBM wanted a single programming language for all users. It hoped that Fortran could be extended to include the features needed by commercial programmers. In October 1963 a committee was formed composed originally of 3 IBMers from New York and 3 members of SHARE, the IBM scientific users group, to propose these extensions to Fortran. Given the constraints of Fortran, they were unable to do this and embarked on the design of a “new programming language” based loosely on Algol labeled “NPL". This acronym conflicted with that of the UK’s National Physical Laboratory and was replaced briefly by MPPL (MultiPurpose Programming Language) and, in 1965, with PL/I (with a Roman numeral “I” ). The first definition appeared in April 1964.
IBM took NPL as a starting point and completed the design to a level that the first compiler could be written: the NPL definition was incomplete in scope and in detail. Control of the PL/I language was vested initially in the New York Programming Center and later at the IBM UK Laboratory at Hursley. The SHARE and GUIDE user groups were involved in extending the language and had a role in IBM’s process for controlling the language through their PL/I Projects. The experience of defining such a large language showed the need for a formal definition of PL/I. A project was set up in 1967 in IBM Vienna to make an unambiguous and complete specification. This led in turn to one of the first large scale Formal Methods for development, VDM.
The language was first specified in detail in the manual “PL/I Language Specifications. C28-6571” written in New York from 1965 and superseded by “PL/I Language Specifications. GY33-6003” written in Hursley from 1967. IBM continued to develop PL/I in the late sixties and early seventies, publishing it in the GY33-6003 manual. These manuals were used by the Multics group and other early implementers.
The first compiler was delivered in 1966. The Standard for PL/I was approved in 1976.
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