S, or Serial port , is used to attach external mice, keyboards, or other devices. Most notebooks have a serial port. P, or Parallel port , is used by most printers and many network connections. Most notebooks have a parallel port. M port is used to attach an external Monitor.
Most notebooks have a monitor port .
Most notebooks have this port, because this frees up the serial port for some other use. A is an Audio port . This means the notebook can accept input from a microphone or can transmit sound out via headphones or external speakers. If the notebook has more than one Audio port, it can support some combination of audio capabilities. MI means a specific audio port, namely one that accepts Microphone Input.