title: Difference between `/dev/ttyS0` and `/dev/ttys0`?
body: <p>In Linux, what is the difference between <code>/dev/ttyS0</code> and <code>/dev/ttys0</code>?</p>
  
  <p>I know that the first is a serial port, but what about the second, with the small <code>s</code>?</p>