An operating system (OS) is a software program, but it is different from word processing programs, spreadsheets, and all the other software programs on your computer. The OS is a software that controls the system's hardware, and which interacts with the user and application software. In short, the operating system is the computer's master control program. The OS provides you with the tools (commands) that enable you to interact with the PC. When you issue a command, the OS translates it into code that the machine can use. The OS ensures that the results of your actions are displayed on screen, printed, and so on. The operating system also acts as the primary controlling mechanism for the computer's hardware.

The operating system performs the following functions:

1. Provides the instructions to display the on-screen elements with which you interact. Collectively, these elements are known as the user interface.
   
2. Loads programs (such as word processing and spreadsheet programs) into the computer's memory so that you can use them.
   
3. Coordinates how programs work with the CPU, RAM, keyboard, mouse, printer, and other hardware, as well as with other software.
   
4. Manages the way information is stored on and retrieved from disks.
   

The functioning of the OS can be extended by adding utility software.