The three machines

Three computers have carried this story so far, and it is time to say what they have in common.

Molly’s laptop, the one with the route page and the View Source adventure, runs WindowsConcept · lights on your mapWindowsMicrosoft’s operating system, dominant on office and consumer PCs. One of the big three, with macOS and Linux.. Finn’s machine at the office above the bakery is a Mac, which is to say it runs macOSConcept · lights on your mapmacOSApple’s operating system for Mac computers, common among developers and designers. One of the big three, with Windows and Linux.. And the servers, the far-away machines that have answered every request in this story, run LinuxConcept · lights on your mapLinuxA free and open-source operating system running the overwhelming majority of the world’s servers. One of the big three, and Android is built on it., as does nearly every server on earth, a fact that surprises people who have only ever met computers with their own screens.

What an operating system actually is

All three are the same kind of thing: an operating systemConcept · lights on your mapoperating systemThe foundational software managing a computer’s hardware and giving applications a standard environment to run in. It divides processor time and memory among programs and controls their access to storage and network., the landlord of the machine. Applications do not touch the hardware — they ask the landlord. The landlord divides the machine’s attention among everything running, hands out memory, guards the disk and the network, and evicts the misbehaving. Traversal’s code never chooses which chip it runs on. It rents, through the landlord, like everything else.

Each running program, to the landlord, is a processConcept · lights on your mapprocessOne running instance of a program, with its own memory walled off by the operating system. The program is the stored software; the process is that software actually running.: the program, alive, with its own walled-off memory. The timing ingest service is a process on some Linux machine right now, idling through week eight, waiting for its one big day. Inside a process, smaller strands of simultaneous work are threadRecognition — just know it existsthreadA smaller sequence of work inside a process, sharing its memory. A process can run several at once, which is how one program does simultaneous things at the same moment., a word this path has been saving for exactly this address: threads live inside processes, processes live under landlords, and landlords come in three names you can now drop correctly into any meeting.

Next: what the landlord is actually dividing up, and what it costs to rent more of it.