5. Some key differences include inputs, outputs, and uses. A PLC has been designed for the factory floor, so it does not have inputs such as keyboards and mice (although some newer types can). They also do not have outputs such as a screen or sound. Instead they have inputs and outputs for voltages and current. The PLC runs user designed programs for specialized tasks, whereas on a personal computer it is uncommon for a user to program their system.
6. This helps detect faulty hardware or software. If an error were to occur, and the PLC continued operating, the controller might behave in an unpredictable way and become dangerous to people and equipment. The self check helps detect these types of faults, and shut the system down safely.