The CPU (central processing unit), or processor, is located on the motherboard inside the computer case. It is often called the brain of the computer because it carries out commands. When you press a key, click the mouse, or open an application, you are sending instructions to the CPU.

The CPU is a small ceramic square with a silicon chip inside. The chip is about the size of a thumbnail. The CPU fits into a socket on the motherboard and is covered by a heat sink, which absorbs heat to keep it cool.

A CPU’s speed is measured in megahertz (MHz), meaning millions of instructions per second, or gigahertz (GHz), meaning billions of instructions per second. Faster CPUs process instructions more quickly. However, the overall speed of a computer depends on several components, not just the CPU.