primary partition
In the context of Boot Manager, a fixed disk partition which contains a single logical drive, and on which an operating system may be installed. Only one primary partition may be active (visible) on a fixed disk at any one time; other primary partitions are hidden from the operating system. Operating systems such as DOS and OS/2 Version 1.x require a primary partition for their installation; OS/2 Version 2.0 may be installed on a primary partition or an extended partition.