Scheduler
The kernel component deciding which process runs next, and for how long.
On a machine with more processes than cores, something has to choose. The choice trades off goals that pull in opposite directions: high throughput wants long time slices and few switches, while low latency wants short ones. Fairness between users conflicts with prioritising whatever matters most right now.
Most processes are I/O-bound and block voluntarily well before their slice expires, which is why an interactive system usually feels fast even under load. Linux used CFS for over fifteen years and switched to EEVDF in kernel 6.6. Real-time processes are handled by separate classes that always precede ordinary ones.