Mac OS X Internals: A Systems Approach

2.2. Bootloader

The bootloader on the PowerPC version of Mac OS X is called BootX, which resides as a single file on the file system. Open Firmware loads it from a bootable device, which could be a locally attached storage device or the network.^[5] BootX contains code that runs in the Open Firmware runtime environment. It performs a sequence of steps to arrange for the Mac OS X kernel to run, and it eventually launches the kernel. We will look at the structure and operation of BootX in Section 4.10.

^[5] In the context of network booting, we treat the network as a bootable device.

The x86 version of Mac OS X uses a bootloader called boot.efi, which is an executable that runs in the EFI environment. Its purpose and operation are very similar to those of BootX.