Back in the days then Parallel ATA (PATA) ruled. I was managed to salvage quite a lot CD/DVD and HDD units. I was looking for a missing pin 21. If you try to force the ATA plug on the hard disk the wrong way around, the gap called "KEYPIN" (pin 20 on the plug) pushes pin 21 of the PATA socket and bends it aside. This pin is responsible for DMA requests of the unit. The disk can no longer reach the host with its requests. The result is a communications problem. Windows switches into PIO mode. The unit will be very slow. And the dumpster is next. I most cases I could fix this with some soldering. Going through the HDD afterwards was always fun. As most of them was not formated.