Processor (CPU)

The CPU (central processing unit) is where instructions actually run. It fetches one tiny instruction, executes it, and moves to the next — billions of times each second. It is not smart: it never guesses, never gets bored, never skips a step.

Inside, it is nothing more than billions of AND/OR/NOT logic circuits etched into silicon. Every app you've ever used is, in the end, this one relentless loop of fetch-execute-repeat.