The operating system is the program that manages all the hardware and software. It is a very advanced application made up of many different programs. It also uses componets from the installed programs that you use in order to create links between the componets.

When you start the computer after the POST the operating system is the first program to load. The first part is stored in a special part of the hard drive called the boot sector. It holds the files that load the operating system.

The operating system has to understand all of the special code for each of the pieces of hardware (called machine language) so that the programs do not have to. The programs can then pass their code through the operating system making the computer easier to use.

The operating system is the first thing that needs to be placed on the hard drive. If a computer does not have a hard drive then the user can use a boot floppy and use a DOS (disk operating system). This just means that it is loaded off of floppies instead of permanent storage. This is how all computers used to be.

Once the operating system has started and in some cases done security authentication's other applications can use the hardware.