Vista is the computer's operating system (OS). It is responsible for many things that happen behind the scenes such as allocating and freeing memory, managing the connection between applications programs and hardware (such as printers, hard drives, monitors, etc.). These are the basic functions of all operating systems for the last 40 years or so. However, modern OSs do so much more. For example, them manage how to have more than one program running at once by dividing up the available system resources (such as the CPU, the memory, etc). They also manage connections to networks and provide a lot of user interface functionality. There is a lot of stuff behind the scenes that you'll never see unless you learn how to become a programmer.