All I/O operations are memory-mapped. There are no port-based I/O instructions. Memory-mapped ports often have different properties than normal RAM:
* The contents of a port can be updated by the hardware. Reading a port will not always return the same value each time it is read.
* It is also possible that reading a port will alter its contents, or alter the contents of other related ports.
* A read-only port is what it sounds like. Attempting to write to this address will not affect the contents.
* A write-only port can be written to, but reading it will result in undefined behaviour.
* Using the ports with instructions other than the Load/Store ones can be very unintuitive.
This is not all negative though. Memory-mapped I/O means that: