CPU · Central Processing Unit
The CPU is the chip that actually does the computing — the brain of the machine. Every instruction in every program you run, from adding two numbers to drawing a pixel, ultimately gets carried out here, one tiny step at a time. What makes it feel magical is sheer speed: a modern CPU runs billions of these little steps every second, so a mountain of trivial operations adds up to a smooth video, a fast page load, a game that responds the instant you move.
On its own, the CPU is surprisingly simple-minded. It mostly just fetches an instruction, does it, and grabs the next — fetch, do, repeat, forever. The cleverness you see on screen comes from stacking billions of those dumb little steps into something useful. Programs live in RAM; the CPU reaches into that fast workspace to grab the next instruction and the data it needs to work on.
Modern CPUs pack several 'cores', and each core is essentially its own little brain that can work on a different task at the same time. That's why a 'quad-core' chip can keep your music playing, your download going, and your editor responsive all at once — four workers instead of one, each chewing through their own pile of instructions.
$ nproc 8 $ uptime load average: 2.14, 1.98, 1.75
nproc counts the cores (here 8); the load average hints how busy they've been.
'Clock speed' (e.g. 3.5 GHz) is how many of those tiny steps a core can take per second — 3.5 GHz is about 3.5 billion. More cores and faster clock both help, in different ways.