IBM 810MB hard drive, pulled from a ThinkPad 755CX.
I believe it's internally an IDE drive, but I'm not sure. I would have to pull the plastic case off to see the drive interface, which might be a destructive procedure.
The drive is too thick for my other machine of the era, a 760XL. This surprises me, because the 760XL is actually thicker, but it's got the memory slots in that area, unlike the 755CX. I have no information on compatibility with other machines.Tested using the aforementioned ThinkPad. This drive boots Linux version 1.3, from 1997. I have not logged in and looked at the system. Ordinarily I would wipe the drive out of a sense of professional courtesy, but at a certain point I feel like historical interest outweighs that. (I may try to hook the system up to a network and archive the drive -- it seems like it might be of some interest to future archaeologists.)
The drive boots in my test machine, but given its age, I wouldn't count on that continuing. Sold as vintage hardware, unwarrantied, unwarrantable.