Apple Partition Map

The Apple Partition Map ( APM short ) denotes a partition table for m68k and PowerPC-based Apple computers. It was introduced with the Macintosh II in 1987 and replaced in 2006 with the transition to Intel architecture with the GUID Partition Table (GPT ).

For addressing a storage medium is divided into logical blocks of usually 512 bytes, where the first data block block 0, the Apple-specific "Driver Descriptor Map" and contains from the second data block, the actual partition table begins. In this, the individual blocks are defined on 32-bit wide addresses, resulting in a partitionable total size of TiB 2 maximial results.

As a special feature of the APM partition table is that it also defines itself as a partition is defined as free memory on the storage medium as a special partition. This is inherent in the medium of a partition with the exception of block 0 of each logical block.

Also on hybrid CDs found APM together with the ISO9660 file system use to ( with Joliet extension like Microsoft ) to provide interoperability at the same time full functionality.

Intel -based Macs

For access to partitions and the file systems contained 10.4 "Tiger" both APM - and GPT - partitioned storage media can be used in the usual way from Mac OS X. However, for the operating system start (boot) on PowerPC-based Macs APM condition, whereas is used on Intel-based Macs GPT.

Macintosh computers that shipped with Mac OS X 10.4 " Tiger" or 10.5 " Leopard", can launch both APM - and GPT - partitioned storage media provided that the method is supported and a suitable operating system is included. This condition is the compatibility of operating systems for both PowerPC and Intel Macs owed ​​because the installation media these Mac OS X versions, using an APM partitioning to (have to) on PowerPC-based Macs to remain bootable. On Intel-based Macs denied the installer yet the selection an APM partition as the installation target. Only for external storage media is an official instructions from Apple on how to install a Mac OS X 10.5 operating system on an APM - partitioned external hard drive that is bootable on both architectures.

Construction

Has an entry in the partition table each have a size of a data block, which usually corresponds to 512 bytes. Each entry in the partition table thus occupies 512 bytes or one sector. Since the partition table is also an entry itself, are the size of the first partition before the possible number of partitions per se. Normally, the partition table itself comprises 63 blocks (sectors), so it can accommodate 62 additional partitions. Together with the driver 64, the first descriptor Map sectors ( 64 × 32 = 512 kB) are assigned in the normal case so.

Each entry in the partition table contains the boot sector and the size of a name, a type, the position of the data provider and a possible start program and the total number of partitions in the partition table. To know, for example, the firmware while reading the first partition entry as many other sectors à 512 bytes must be read yet, so that all entries have been processed.

Partition Types

Partition status

73205
de