Originally Posted by
ve3id
'access the I/O ports directly': this needs a bit of explanation! If you are in kernel mode on any fit-for-use operating system, you can always access the I/O ports directly - how else do you do I/O at all? Or are you confusing the inadequacies of MS Windows of the 20286 era with the hardware itself?
I am sure nobody in the aviation world uses MS Windows on control computers - typically fail-safe control strategies involve three computers, all voting for control (to avoid byzantine failures) , and each of different binary compatibility and O/S origins, all running the same well -tested algorithm using different languages.
With modern CPUs the I/O ports are on the same bus as the memory. The instruction set is backwards compatible so old software can still work the same way as before. However the modern architecture supports a new feature: I/O devices can read and write directly from/to memory, bypassing the CPU, which can be a huge benefit reducing CPU load during large I/O operations.