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Mac OS ROM Image File Contents

The Mac OS ROM image file (also called the bootinfo file) contains three main components, each of which is made up of smaller components: the pieces that are part of the bootinfo specification, the Trampoline code, and the Mac OS ROM Image itself.

Most changes needed for a new CPU occur in the boot ROM, not in the bootinfo file. Changes to the Mac OS ROM Image should be limited to new manager software and support for hardware that is common to many Macintosh computers (ATA interface modules, user interface modules, and the like).

The bootinfo file exists on the boot device and has a localizable name. Identification information that leads to the file's path is stored in NV-RAM and the search algorithm for a usable bootinfo file parallels the search mechanism across SCSI, ATA, and so forth, used in the former startup disk routine. By default, the file is located by using the directory ID of the "blessed folder" in the boot block of each HFS or HFS Plus partition, and then searching for a file with a file type of 'tbxi' . Searching by file type is done to allow localization of the file. Nonlocalized, the name of the bootinfo file is "Mac OS ROM".

Trampoline Code

Mac OS ROM Image