The CPU is the "brain" of your PC that controls your entire system including all peripheral devices. Anybody that wants to do anything, must first check in with the CPU first. The CPU is an integrated circuit called a microprocessor.

Historically, CPUs were large affairs and very costly to make. But, with the invention of the integrated circuit in the 1970s, CPUs shrunk dramatically, and became very cheap to make.

Your PC's CPU is a very complex piece of engineering. It contains hundreds of thousands to millions of circuits on a single chip. A new generation is created about every two years.