That part of the hard disk containing the operating system to be loaded when you start or restart the computer. You can install 2 different operating systems ( perhaps DOS and OS/2) on your hard disk, but each must be in its own separate area, or partition. Only one partition can be active at any given time, and to change from the DOS to the non-DOS partition, you may have to use the DOS FDISK command.

A section of the computer's memory that houses the operating system being used.

The partition where the computer starts up. The active partition must be a primary partition on a basic disk. If you use one Windows operating system exclusively, the active partition can be the same as the system partition. If you have a dual-boot system with two operating systems (such as Windows 2000 and Windows NT OR Windows NT and Windows 98® or MS-DOS®) the active partition must contain the startup files for both operating systems. See also Basic disk, Extended partition, Extended partition, Partition, Primary partition.