Parts of a Hard Drive – Platter, Spindle, Head, Actuator

All 11 parts on the diagram

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Cover off 8

Platter A rigid disk with a magnetic coating. It stores the data.
Spindle It holds the platters and its motor spins them.
Track One ring of data on the surface of the platter.
Read/write head It reads and writes data as the platter spins under it.
Actuator arm It swings the head across the platter to the right track.
Actuator (voice coil) A coil beside a magnet. Current in it swings the arm.
Magnet A strong fixed magnet. The coil moves in its field.
Air filter It traps dust from the air moving inside the drive.

Underneath 3

Circuit board The drive's electronics. They control the motor and the actuator.
Data connector The data cable from the computer plugs in here.
Power connector The power cable plugs in here.

How this list was compiled: Every name checked on 2026-09-30, a name kept only where two independent sources use it. (1) Wikipedia, Hard disk drive, text only, https://en.wikipedia.org/wiki/Hard_disk_drive (platters on a spindle; magnetic heads on a moving actuator arm; the actuator is a moving coil and permanent magnet motor, the voice coil; a fixed magnet above and below the coil; the recirculation filter; the drive's electronics control the actuator and the disk's rotation; printed circuit board; data and power connectors; tracks). (2) R. and A. Arpaci-Dusseau, Operating Systems: Three Easy Pieces, chapter Hard Disk Drives, a free university textbook, https://pages.cs.wisc.edu/~remzi/OSTEP/file-disks.pdf (platter, surface, spindle and its motor, track as one concentric circle of data, disk head, disk arm). (3) Scott Mueller, Upgrading and Repairing PCs, sixth edition, chapter Hard Disk Drives, read as full text at https://archive.org/details/URP_6th_edition (platters, read/write heads, head actuator and voice coil actuator with its stationary magnet, air filters and recirculating filters, spindle motor, logic boards, interface and power connectors, tracks). No maker is named in the copy or drawn. Licence: own work

The drawing: Drawn for this site on 2026-09-30 from plain geometry; nothing traced. Licence: own work

How it works

The parts of a hard drive, with the cover taken off. Data is kept on a spinning platter and is read by a head on the end of a swinging arm. The second view shows the electronics underneath.

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Cover off, from above

Numbers 1 to 8: the platter, the spindle at its center, one track, the read/write head on the end of the actuator arm, the actuator and its magnet in the corner, and the air filter. Real tracks are far too narrow to see: hundreds fit in the width of a hair.

Underneath

Numbers 9 to 11: the circuit board and, on its back edge, the data connector and the power connector.

Most drives stack several platters on one spindle, with a head for each surface.

Questions and answers

What are the main parts of a hard disk?

One or more platters on a spindle, a read/write head for each platter surface, an actuator arm that carries the heads, the actuator that swings the arm, and a circuit board. The platters, heads and actuator are sealed inside the case.

How does a hard drive read data?

The spindle motor spins the platters. The actuator swings the arm until the head is over the right track, and the head reads the magnetic pattern as it passes underneath.

What is the voice coil in a hard drive?

The moving part of the actuator: a flat coil on the back of the arm, lying beside a fixed magnet. Current in the coil pushes it one way or the other, which swings the arm. The name comes from the coil in a loudspeaker.

What does the circuit board on a hard drive do?

It holds the electronics that control the spindle motor and the actuator, and it passes data between the heads and the computer.