Since 1.3, the system software supports the initialization of ROM drivers
residing on expansion peripherals, including the ability for drivers to
provide a DOS node which the system can boot from. This feature is known
as Autoboot.

Automatic boot from a ROM-equipped expansion board is accomplished before
DOS is initialized.  This facility makes it possible to automatically boot
from a hard disk without any floppy disks inserted.  Likewise, it is
possible to automatically boot from any device which supports the ROM
protocol, even allowing the initialization of a disk operating system
other than the Amiga's dos.library.  ROM-based drivers contain several
special entry points that are called at different stages of system
initialization. These three stages are known as DIAG, ROMTAG INIT and BOOT.

 events at diag time    events at romtag init time    events at boot time