Credits: IOP boards provided by Richard, 4 Pi board from @tubetime.Photo of the IOP and CPU courtesy of RR Auction. IOP documentation from Mike Stewart. Exploded diagram from https://ibiblio.org/apollo/Shuttle/IBM-74-A31-016%20-%20Space%20Shuttle%20Advanced%20System,%204%20Pi%20-%20Prototype%20Input,%20Output%20Processor%20(IOP).pdf#page=145