hard driver power and ground question?

Question

the 4 pin connector for power and ground on the back of the hard drive, what is the 5v power supply do or run in the hard drive?

Answer 1

there are multiple components ... the drive motor, the arm positioning device, and (maybe) another device which locks down the drive when at zero rpm (transportation safety).

plus the electronics that respond when the computer tries to say "Hi! who are you??"

:-)