Apple Partition Map (APM) is a partition scheme used to define the low-level organization of data on disks formatted for use with PowerPC Macintosh computers.
Apple disks are divided into logical blocks, with 512 bytes usually[1] belonging to each block. The first block contains an Apple-specific Block0 structure.
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 Macs
Intel-based Macs computers can boot Mac OS X from APM disks[2], but when run on an Intel-based mac, the installer for Mac OS X only allows the system to be installed on GUID Partition Table disks.[3] Otherwise APM disks can be used normally. PowerPC-based systems can only boot Mac OS from APM disks, but otherwise can use GUID Partition Table disks normally.[4]
References
- ^ Almost all hard-disk drives use 512-byte blocks. Some Solid-state drives do not. When unsure, DKIOCGETBLOCKSIZE should be checked.
- ^ http://support.apple.com/kb/HT2595
- ^ http://www.macosxhints.com/article.php?story=2007102511133285
- ^ http://lists.apple.com/archives/Macos-x-server/2006/Apr/msg01335.html
External links
- Structure of the Apple partition map, on Apple Developer Connection
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