I know I have seen these but haven't been able to find one. I have several of the adapters for putting the laptop drive on a regular 3.5" / PC ribbon cable, but I need to go the other way around:
Proprietary 3x44pin header on motherboard goes to a 2nd card/drive mount, and the drive mount has one slim notebook optical connector on the top and the mini 44? pin header on the bottom for mounting a laptop drive. I made room for the full size 3.5" drive elsewhere (since it's not fun / cost effective looking for 7200rpm ATA 2.5" drives any more) and obviously 3.5" 7200 PATA drives are the opposite, to the point of being disposable.
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