Could you explain in more detail how these trigger a reboot? From writing a 32-bit kernel I understand how the triple fault method is supposed to work, for example, but would love to know a little more about these methods.
int 19 should just execute code in the BIOS that triggers a reboot. Setting CS and jumping is re-entering the BIOS at the same entry point as at power-on. The BIOS should then reinit all the hardware.