The motor in the hard drive is a three-phase AC motor, with three wires, with four wires. The coil connection mode is star. The 3-wire is used to seal the neutral line inside the motor. This is the neutral line for a 4-wire. And this motor is hall free, by U,V,W 3 coil surge to measure speed and self-test phase. The hard drive has a drive chip on it. Because the hard disk motor belongs to a precision motor. Very high speed requirements. So most of the driver chips are programmed to turn.