In RISC OS, PCI devices can be identified in one of two ways. Users generally
need only be aware of the PCI system when expansion cards are added to the
machine, and will use the PCI slot number, in commands like *Unplug or
*PCIDevices. Slot numbers are fixed for a given system.
Device drivers use a PCI handle - each function of each PCI device in the
system is given a unique, permanent non-zero handle when it is discovered.
Handles remain constant as long as the device remains present in the system,
but can change when the system is rebooted, or if a card is removed and
reinserted (if the system supports hot-plugging).
Handles do not change if the PCI Manager is reloaded. Handles are assigned
from 1 upwards, so can be searched linearly, much like Expansion Cards.
A value of 0 is not valid, so if PCI_FindByID or PCI_FindByLocation or PCI_FindByClass don't find anything the handle returned is zero.
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