Essential Computer Hardware

Inside the CPU

This is a die shot of an old Pentium CPU. Note the marked sections.

At the top you can also see the clock. The clock sets the rate at which the computer executes instructions and is usually measured in GigaHertz (GHz). This is how CPUs are rated.

On each clock cycle, the control unit fetches and decodes an instruction; this is called the instruction cycle.

Then the arithmetic logic unit executes the instruction and stores the data; this is called the execution cycle.

This cycle happens billions of times a second. So a 2 GHz CPU can execute 2 billion instructions a second.