Interestingly, in this case I can connect the hard disk to the adapter in two ways: namely, when the two free pins are on the right side of the adapter connector and when they are on the left side. From what I've read, the M/S setting actually has no effect on disk performance, it only serves the same function as e. IDE HDDs do indeed use a 44-pin connector which integrates both IDE and power (see pinout); if the extra 4 pins remain unconnected the disk would have no power.

USB to IDE SATA 2.5 3.5 Hard Disk HDD Cable Converter USB to IDE SATA 2.5 3.5 Hard Disk HDD Cable Converter

But assuming it's standard IDE + proprietary extra stuff, then it should still have the "key pin" in the same position, and the connector should only fit one way. With only a single drive connected, I don't think it matters at all (the purpose of these jumpers is when you have two IDE devices on the same cable), but either "Master" or "Cable Select" is typical in this situation. this case I can connect the hard disk to the adapter in two ways: namely, when the two free pins are on the right side of the adapter connector and when they are on the left side. Furthermore, the IDE connector on the USB/IDE converter doesn't fit for all my IDE hard drives: on one of the drives 2 pins remains free on the IDE hard drive, they have no corresponding holes on the adapter connector part.

I have no clue how to place the jumper settings on the IDE hard drives: slave, master or cable select? The cheap Gembird IDE-to-USB adapter that I recently bought has two IDE connectors: 40-pin on one side for desktop 3.