Multi-tasking

Multi-tasking is when the operating system manages many tasks so that they appear to happen at the same time. A single CPU core can carry out only one process at a time, so the operating system rapidly switches between processes to create that effect.

The operating system decides which process runs next and for how long. The CPU carries out the instructions of whichever process is running, while the operating system manages the switching. Each process gets a short turn; when its turn ends, it is paused and another process is allowed to use the CPU. The first process can be resumed later, so being paused is not the same as being closed.

For example, a gym treadmill may update the distance display, check the heart-rate sensor and play a sound when a button is pressed. The operating system might let the display process run, then switch to the heart-rate process, then to the sound process, then back to the display. The changes happen so quickly that the treadmill seems to do all three at once, even though the CPU is only working on one process at any moment.