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Semicolony ELI5 · comic

Concurrency vs parallelism.

Interleaving tasks so nothing stalls, versus literally doing two at once — a skill versus a head-count.

  1. All three of you: soon.
    3 orders
    1

    Three customers were promised progress, and one pair of hands has to deliver it.

  2. Drip, you’re on your own.
    brew froth
    2

    Every switch happens at a wait — the espresso drips just as well unsupervised.

  3. one worker, taking turns
    3

    Zoomed in, the truth shows: never two things in the same instant, never anyone abandoned for long.

  4. Together — pour.
    same instant!
    4

    Here is the line switching can never cross — two pours in one instant takes a second barista.

  5. four cores, four at once
    5

    Extra cores pay off only when there is computing to split; they do nothing for time spent waiting.

  6. You arrange; I assign.
    tasks core core runtime spreads
    6

    You write the interleaving; the runtime decides the head-count, spreading tasks over whatever cores exist.

One barista juggling many orders by switching, versus several baristas pouring at the same instant.
Semicolony semicolony.dev/eli5/concurrency-vs-parallelism/comic
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