The most ancient laptop I ever touched was a Compaq 386/16 with a 20MB 3.5" 1/2 height IDE drive. It sounds pretty much like the same, or probably the piece of crap I had was a predecessor. I do remember it was clearly a 20MB drive though. I swapped it for a regular desktop 40MB IDE that we had in the shop.
Everything I found about that series says it's IDE. I couldn't find anything specifically saying the physical size, but I suspect it was a 3.5" drive. I seriously doubt it was RLL, MFM, ESDI, or anything more exotic. So he's wasting everyone's time asking rather than just opening it up and seeing "ooh, a IDE drive." Even if it was, he could go find some combination of adapters to use it. Anyone who's worked with stuff long has a box full of adapters and cards for exactly this. Well, I did ditch all my ancient cards on eBay a few years ago.
I'd be surprised if the drive even spins though. Most of the time when I go to try ancient hardware, the drives don't spin, or spin enough, even though the owner remembers that it was working when they shut it off.