I know that with plcs and local chasis IO the first slot is always zero and the plc uses it but when talking about point io and flex io is the adapter considered slot 0 or is the first io module slot 0? Or is there even a slot zero when talking abou these systems?
You have generalised too much, and it is important to understand the difference between a "slot" being a physical place, and a Slot being an addressed place...
In the Allen-Bradley world...
PLC5 : The PLC5 processor has it's own dedicated place in the 1771 chassis on the left, and is not called a "slot" at all, the following module locations are "slots" and are sequentially numbered, starting at 0, according to the rack-addressing mode.
SLC : The SLC processor has it's own dedicated place in the 1746 chassis on the left, the following module locations are "slots" and are sequentially numbered, starting at 0.
CompactLogix : There is no "chassis" as such. The processor has two "busses" emanating from it. Comms and special modules build from the left of the processor module. I/O modules build from the right. In either case, the module's "slot number" is sequential, starting from 0.
ControlLogix : The 1756 chassis has no dedicated slots for anything, it is just a communications bus that allows any mix of Controllers, I/O modules, and Communications modules, in any slot(s). This is the only case where the slot's physical location matches it's "slot address"
