Section 12.4. Reserved Areas

12.4. Reserved Areas

The first two logical sectors (1024 bytes) and the last logical sector (512 bytes) of a volume are reserved. Although Mac OS X does not use these areas, they were used by earlier Mac OS versions.

The 1024-byte reserved area at the beginning of a volume was used as boot blocks. These blocks contained information necessary to boot the system, including the entry point to the boot code and names of several critical files, for example:

• System file (typically System)

• Shell file (typically Finder)

• First debugger installed during startup (typically Macsbug)

• Second debugger installed during startup (typically Disassembler)

• File containing the startup screen (StartUpScreen)

• System scrap file (Clipboard)

The boot blocks also contained configurable system parameters such as the maximum number of open files allowed, the fraction of physical memory to be used for the system heap, and the number of event queue entries to allocate.

The 512-byte reserved area at the end of a volume was used by Apple during system manufacturing.