@dhoelzer, Chuck(G), Iowen.
Thank you all for the response, it is a pity that it is not a harddisk interface.
>> How does it lock into the frame
Just like the other boards, only a little shorter, it is floating in the card cage.
>> But it could be a simple parallel interface; the photos don't give much idea of what chips are used,
Most of the text on the chips is removed, it looks like TTL
Have you seen the unpopulated connector in the top left corner with the text: Remote Display
Could it be a scanner or printer interface ?
Hans01