I think the early Sony 3.5" drives used a 26-pin
header arrangement
to answer someone else's question.
Certainly some early Sony 3.5" drives used a 26 pin header. They exist in
both single and double sided versions, and IIRC there are subtle changes
to the interface btween them (the single-sided one uses 1-of-n select
lines, the doublesided one has 2 lines binary-encoded).
These drives (often?) rotate at 600rpm, and can't easily be replaced with
PC drives.
-tony