The transputer and occam: A personal story

Abstract The paper tells the story of the development over twenty‐five years of my ideas about communicating sequential processes. One of its most subtle and most useful facilities is the guarded choice, which appears as the ALT command in occam. Its subtleties are clarified and its usefulness increased by an understanding of the relevant simple algebraic laws, based on mathematical research conducted at Oxford. The abstractions provided by mathematics are the secret of the versatility of occam, which can be reliably and efficiently implemented by multiprogramming or by multiprocessing or by hardware, or by any combination of these. In conclusion, it is conjectured that the occam programming paradigm will remain the most efficient and most reliable for the general‐purpose shared‐store multiprocessors of the future.