Apple Partition Map is a partition scheme used to define the low-level organization of data on disks formatted for use with 68K

68k

The Motorola 680x0/m68000/68000 is a family of 32-bit CISC microprocessors. During the 1980s and early 1990s, they were popular in personal computers and workstations and were the primary competitors of Intel's x86 microprocessors...

 and PowerPC

PowerPC

PowerPC is a RISC architecture created by the 1991 Apple–IBM–Motorola alliance, known as AIM...

 Macintosh

Macintosh

The Macintosh , or Mac, is a series of several lines of personal computers designed, developed, and marketed by Apple Inc. The first Macintosh was introduced by Apple's then-chairman Steve Jobs on January 24, 1984; it was the first commercially successful personal computer to feature a mouse and a...

 computers that was introduced with the Macintosh SE

Macintosh SE

The Macintosh SE was a personal computer manufactured by Apple between March 1987 and October 1990. This computer marked a significant improvement on the Macintosh Plus design and was introduced by Apple at the same time as the Macintosh II....

 (it can be used on a Macintosh Plus

Macintosh Plus

The Macintosh Plus computer was the third model in the Macintosh line, introduced on January 16, 1986, two years after the original Macintosh and a little more than a year after the Macintosh 512K, with a price tag of US$2599...

 too).

Apple disks are divided into logical blocks

Logical block addressing

Logical block addressing is a common scheme used for specifying the location of blocks of data stored on computer storage devices, generally secondary storage systems such as hard disks....

, 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

Tebibyte

The tebibyte is a standards-based binary multiple of the byte, a unit of digital information storage. The tebibyte unit symbol is TiB....

.

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

ISO 9660

ISO 9660, also referred to as CDFS by some hardware and software providers, is a file system standard published by the International Organization for Standardization for optical disc media....

 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 Mac computers can boot Mac OS X

Mac OS X

Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...

 from APM disks, 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

GUID Partition Table

In computer hardware, GUID Partition Table is a standard for the layout of the partition table on a physical hard disk. Although it forms a part of the Extensible Firmware Interface standard , it is also used on some BIOS systems because of the limitations of MBR partition tables, which restrict...

 disks. Otherwise APM disks can be used normally. PowerPC-based systems

Power Macintosh

Power Macintosh, later Power Mac, was a line of Apple Macintosh workstation-class personal computers based on various models of PowerPC microprocessors that were developed, marketed, and supported by Apple Inc. from March 1994 until August 2006. The first models were the Power Macintosh 6100,...

 can only boot Mac OS

Mac OS

Mac OS is a series of graphical user interface-based operating systems developed by Apple Inc. for their Macintosh line of computer systems. The Macintosh user experience is credited with popularizing the graphical user interface...

 from APM disks, but otherwise can use GUID Partition Table

GUID Partition Table

In computer hardware, GUID Partition Table is a standard for the layout of the partition table on a physical hard disk. Although it forms a part of the Extensible Firmware Interface standard , it is also used on some BIOS systems because of the limitations of MBR partition tables, which restrict...

 disks normally.

Partition identifiers

File system	Identifier
Be File System Be File System The Be File System is the native file system for the BeOS....	Be_BFS
ext2 Ext2 The ext2 or second extended filesystem is a file system for the Linux kernel. It was initially designed by Rémy Card as a replacement for the extended file system .... /A/UX A/UX A/UX was Apple Computer’s implementation of the Unix operating system for some of their Macintosh computers. The later versions of A/UX ran on the Macintosh II, Quadra and Centris series of machines as well as the SE/30. A/UX was first released in 1988, with the final version released in 1995...	Apple_UNIX_SVR2
Hierarchical File System Hierarchical File System Hierarchical File System is a file system developed by Apple Inc. for use in computer systems running Mac OS. Originally designed for use on floppy and hard disks, it can also be found on read-only media such as CD-ROMs... (HFS)	Apple_HFS

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.