Apple Partition Map

Apple Partition Map (APM) is a partition scheme used to define the low-level organization of data on disks formatted for use with Macintosh computers.

Apple disks are divided into blocks, with 512 bytes belonging to each block. The first block contains driver information. The actual partition map begins at block 1.

The Apple partition map is unusual in that it defines itself as one of the partitions on the disk. This means that every block on the disk (with the exception of the first block, block 0) belongs to a partition.

Some hybrid discs contain both an ISO 9660 primary volume descriptor and an Apple partition map, thus allowing the disc to work on different types of computer, including Apple systems.

Intel-based Macintosh computers can boot Mac OS X from an APM disk or GUID Partition Table (GPT) disk; 68k and PowerPC-based systems boot Mac OS from an APM disk only.

See also

* [http://developer.apple.com/documentation/mac/Devices/Devices-121.html#MARKER-2-27 Structure of the Apple partition map] , on Apple Developer Connection