|
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. It was introduced with the Macintosh II.〔 Disks using the Apple Partition Map are divided into logical blocks, with 512 bytes usually belonging to each block. The first block, ''Block 0'', contains an Apple-specific data structure called “Driver Descriptor Map” for the Macintosh Toolbox ROM to load driver updates and patches before loading from a MFS or HFS partition.〔 Because APM allows 32 bits worth of logical blocks, the historical size of an APM formatted disk using small blocks〔 is limited to 2 TiB.〔 The ''Apple Partition Map'' maps out all space used (including the map) and unused (free space) on disk, unlike the minimal x86 master boot record that only accounts for used non-map partitions. 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 computers, including Apple systems. ==Intel-based Macs== For accessing volumes, both APM and GUID partitions can be used in a standard manner with Mac OS X 10.4 and higher. For starting an operating system, PowerPC-based systems can only boot from APM disks〔 whereas Intel-based systems generally only boot from GUID disks.〔〔〔 However, Intel-based models that came with Mac OS X Tiger or Leopard preinstalled are able to boot from both APM and GUID disks. This is due to the installation media for these versions of Mac OS X, which are APM partitioned in order to be compatible with PowerPC-based systems.〔 Nevertheless, the installation of Mac OS X on an Intel-based Mac demands a GUID partitioned disk or will refuse to continue. Apple never officially supported booting from an internal APM disk on an Intel-based system, but there is an official Apple document describing how to set up a dual bootable external APM disk for use with PowerPC and Intel.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Apple Partition Map」の詳細全文を読む スポンサード リンク
|