The A-0 system (Arithmetic Language version 0), written by Grace Murray Hopper  in 1951 and 1952 for the UNIVAC I, was an early compiler related tool developed for electronic computers. The A-0 functioned more as a loader or linker than the modern notion of a compiler. A program was specified as a sequence of subroutines and arguments. The subroutines were identified by a numeric code and the arguments to the subroutines were written directly after each subroutine code. The A-0 system converted the specification into machine code that could be fed into the computer a second time to execute the said program.
The A-2 system was developed at the UNIVAC division of Remington Rand in 1953 and released to customers by the end of that year. Customers were provided the source code for A-2 and invited to send their improvements back to UNIVAC. Thus A-2 was an early example of free and open-source software.
- Ridgway, Richard (1952). "Compiling routines". Proceeding ACM '52 Proceedings of the 1952 ACM national meeting (Toronto).
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- Hopper "Keynote Address", Sammet pg. 12
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- . 195510.pdf. "PAPERS: Automatic Programming: The A 2 Compiler System -- Part II". Computers and Automation. 4 (10): 15–27. Oct 1955.
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- Hopper, Grace (May 1952). "The Education of a Computer" (PDF). Proceedings of the Association for Computing Machinery Conference (Pittsburgh) May 1952. pp. 243–249. doi:10.1145/609784.609818.
- Hopper, Grace (16 February 1955). "Automatic Coding for Digital Computers" (PDF). High Speed Computer Conference (Louisiana State University) February 1955. Remington Rand.
- Hopper, Grace. "Keynote Address". Proceedings of the ACM SIGPLAN History of Programming Languages (HOPL) conference.
- Ridgway, Richard K. (1952). "Compiling Routines". Proceedings of the 1952 ACM national meeting (Toronto) ACM '52.
- Sammet, Jean (1969). Programming Languages: History and Fundamentals. Prentice-Hall. pp. g. 12.