Audio/Video Glossary - IDBIT/TERMINATIONA computer and a connected monitor identify each other by the ID BITs, which are specific pins of the connectors and cables linking them. Those pins, when connected to a signal common ground (terminated) indicate which monitor is connected, and what signal the computers’ graphics card should output to this specific monitor. A PC VGA system uses pins 4, 11 and 12 as the signaling bits, while a MAC computer uses pins 4, 7 and 10. Some PC notebooks output the VGA signal to an external VGA monitor only when shorting ID BIT pin 4 to ground. In this case, the notebook PC should sense the ID BIT at pin 4 connected to ground at boot-up.