Processes and multitasking — Computing, 11–13
A running program is a process: it has work to do and uses computer resources. An operating system shares time and resources between processes, so several apps can appear to run together.
Several jobs sharing one machine
A process is not just the program file; it is that program while it is running, with its current information and resources. The operating system gives each process turns, rather like a cook switching between dishes without throwing any away.
Why multitasking exists
People want to listen to music, download a file, and write at the same time, but a processor may have only one core available for those jobs. Sharing its time keeps the machine useful instead of making you wait for each task to finish.
Music while a file downloads
Imagine a single-core computer with a music app and a download. For a moment it updates the music, then it starts or checks a download step, then returns to the music; rapid switching makes both seem continuous, while waiting for data leaves the CPU free for other work.
It is not always truly simultaneous
It is reasonable to think two apps run at exactly the same moment because the screen and sound show no obvious pause. On one processor core, they usually take turns; several cores can genuinely work at once, but each core still handles its own instructions in order.
When an app freezes
The operating system can pause or close a process that uses too much memory, waits forever, or stops responding. That protects other work, although the frozen app may lose unsaved information, so saving matters before starting something risky.
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