The CPU runs software. Without software, the computer would not know what to do. Software provides the instructions that the CPU can operate on. There are many pieces of software available and each provide different services and perform different operations.

Computers only understand very simple instructions. All programs are made up of thousands of these simple instructions. The software has to tell the computer to access the hard drive, display graphics and even produce sound. Software to control the computer hardware is normally written in advance and stored on the hard drive. This software is known as the operating system.