Did you search for the jumpers in google? Sometimes, the drives have four choices:
- Master without slave.
- Master with slave.
- Slave.
- Cable select.

Also, keep in mind that the jumpers can be different on every drive, so you MUST look into the HDD label or google you HDD model to find out.

BTW, the end of the IDE cable does matter. If you put both drives on "Cable select", the position will mark which one is master and slave (in any other case, the jumpers will determine if it is master or slave).

Some drives differentiate between "Single or Master" and "Master w/Slave present". Some drives have a jumper setting for Slave while on others the absence of a jumper means Slave. Follow the illustrations on your drive labels carefully. Set the Samsung to "Master" or "Master w/Slave present", depending on how Samsung has it labeled on their drive. Then set the Seagate to "Slave" (which I believe would be no jumpers on a Seagate) and see how it goes.

Alternatively, you can set both drives to "Cable Select", then make sure the end cable (farthest one from the motherboard connection) is going to the Samsun while the middle plug goes to the Seagate. See http://www.pcguide.com/ref/hdd/if/ide/confCS-c.html for more info.

Reading docs is a nice strategy, but as per usual, random fiddling works the best 🤣 As soon as I set Samsung to first pair of pins and removed the jumper from Seagate altogether, the drives set in correctly.

Thanks, everyone!