Dijkstra’s EWD 51 is a structured educational coverage of the workings of semaphores in communicating processes and with IO devices. It is the first part in a series of three articles called MULTIPROGAMMERING EN DE X8″ (Multiprogramming and the X8), EWD54 and 57 describe part 2 and 3.
The X8 is the Dutch research computer for which Dijkstra and hos team developed the operating system, and he was able to test his now famous concepts for multiprogramming.
In a way it is the formal part of the talk that Dijkstra held and was transcribed in EWD 35.
EWD 51 extensively discusses the mechanisms of semaphores, the conditions, and (hardware) implications. That is the summary. To give more would be pointless, and you’d rather read the entire article. (The article is in Dutch – I could provide a quick translation if you are interested. Please let me know through a comment on this post, or send me an email)
The Dutch language used in this article is highly interesting. Dijkstra invents concepts for which no words existed before (seinpaal/semaphore as computing concept to start with) the abbreviations P (prolaag/pass – probeer te verlagen) and V (verhoog/increase), critieke secties / critical sections, ingreep-flip-flop / interrupt-flip-flops, luisterbit / listener bit, doof-horend bit.
The article could still function as a modern introduction into the topic and still be applicable to today’s computers.
So far ahead, so clear, so up to date still.