The order the various probes are compiled in. If you look at the network
probes for example you will see ne2000 is done very early as an ne2000 card
can hang the ISA bus if probed wrongly by another driver
Some of the scsi drivers also have dependencies - the buslogic driver
used to confuse the aha1542 card so aha1542 couldnt depend on it.
Then there are cards that have compatibility modes where we need to probe
them first in their own mode to avoid using a poor driver.