Most operating systems have ways to divide disks into several pieces - so that an entire disk does not have to be devoted to one filesystem, or even to one operating system. This division of the disk is usually called partitioning. In some systems the partitioning information is built into the operating system code, but that tends to be restrictive. In the Mac OS the partitioning information is stored on the first few blocks of the disk.
The Apple disk partition scheme was developed in 1986 by the A/UX team with input from the Mac OS and Apple II teams. There was an earlier partition scheme used in the first SCSI drives on the MacPlus, but that was replaced by the current scheme in the Macintosh II and subsequent machines and in subsequent operating system releases. The current scheme is supported by Mac OS, A/UX, ProDos, Linux, MkLinux and MacOS X.