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ROM program
Can select only a limited number of devices
* two to four disks (rarely more)
* floppy
* only some can boot from CD/DVD
* network devices, etc may add code
Inconsistent between devices/machines
Many boot programs per device
Notes:
A PC's boot program usually is limited
to a small number of potential boot
devices. Older BIOSes support only
two boot disks, while newer ones may
allow four; but often you cannot decide
which disk is the default boot device.
Almost alll PCs with a floppy drive can
boot from it. Some new PCs can't boot
from CDs or DVDs. Only some network
cards support network booting.
In short, there is no consistency across
BIOSes and devices.
On the other hand, PC OSes have to
coexist with each other on the same
disk, so a single disk may have several
boot programs on it.