- Your picture is not too good
- You have not given any notes about where you got this from
I'd hazard a guess that its a SCSI connector.
There are 25 pins on each side (i think) and it looks like it might go well with
the Centronics SCSI 50pin connector from the link I give below.
don't have enough confidence on it yet... the plastics do not match too well.
This cheat-sheet reference should help you try matching better,
and also give you suggestions how to take connector pictures :-)
And, here is a link to the Apple Mac SCSI FAQ for further perusal.
Look for the Internal 50pin SCSI interface.
Update: First-hand-information from kinokijuf indicates it is a PATA connector.
You should re-check based on this detail.