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 68K and PowerPC Macintosh computers that was introduced with the Macintosh II[1].
Apple disks are divided into logical blocks, with 512 bytes usually belonging to each block. The first block contains an Apple-specific Block0 structure. Because APM allows 32 bits worth of logical blocks, the size of an APM formated disk is limited to 2 TiB[2].
The Apple partition map is unusual in that it defines itself as one of the partitions on the disk, and it defines free space as a partition in the map as well. 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.
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[edit] Intel-based Macs
Intel-based Mac computers cannot boot Mac OS X from APM disks. 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.[3]
[edit] Partition identifiers
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This list is incomplete; you can help by expanding it.
| File system | Identifier |
|---|---|
| Be File System | Be_BFS |
| ext2/A/UX | Apple_UNIX_SVR2 |
| Hierarchical File System (HFS) | Apple_HFS |
| Free Space | Apple_Free |
| Partition Map | Apple_Partition_Map |
[edit] References
[edit] External links
- Mac OS: Technical overview of disk volume structures Overview of the elements of a disk volume / partition
- File System Forensic Analysis: PC-based Partitions - Apple partitions Detailed technical analysis of the structure of Apple's partition map.
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