Assembly Line

How hard drives are made

A drive's read-write head flies tens of nanometers above a platter spinning at thousands of revolutions a minute.

stations
6
things upstream
76
raw sources
27
steps from the ground
9

The short version

A hard drive stores data on stacked platters made of aluminum or glass. They are polished until almost perfectly smooth, then sputtered in a vacuum with layers of cobalt-based magnetic alloy and topped with a carbon overcoat. In a cleanroom they are mounted on a spindle with read-write heads, sealed and tested.

  1. Polish the platter blanks

    Disks of aluminum alloy or glass are polished, then mechanically textured with fine grooves that help the magnetic layers stick. Platters are among the smoothest surfaces manufactured anywhere, though not so smooth that the head cannot fly over them.

    Goes in
    AluminumGlass

  2. Sputter on magnetic layers

    In a vacuum, magnetron sputtering coats both sides with underlayers and a recording film of a cobalt, chromium and platinum alloy. Thin layers of ruthenium separate the magnetic sub-layers.

    magnetic film 10 to 20 nm

    Goes in
    CobaltChromiumPlatinum

  3. Add a carbon overcoat

    A diamond-like carbon overcoat is deposited next, and a lubricant goes on top, so the head can survive an occasional touch.

  4. Build heads and arm

    Each read-write head is made on a tiny scale and mounted on an arm moved by a voice coil actuator.

    Goes in
    Steel

  5. Assemble in a cleanroom

    Platters are stacked on the spindle motor, the heads are brought in and a controller board is attached. Platter work is done in cleanrooms often 100 times cleaner than a hospital operating room.

    Goes in
    Printed circuit board

  6. Test the finished drive

    The drive spins up and every region of every surface is tested.

End of the lineHard drive

Worth repeating

  • The protective carbon coat on a platter is diamond-like carbon about 2 nanometers thick.
  • IBM's 350 disk drive stored 3.75 megabytes on 52 disks and was about the size of two large refrigerators.
  • Platters spin at 5,400 or 7,200 rpm in most consumer drives.

Back to the ground

Follow every input upstream and hard drive starts as these 27 raw sources.

Crude oilCoalSilica sandLimestoneCobalt oreChromiteAirWaterPlatinum oreBauxiteRock saltTronaSulfurNatural gasIron oreDolomiteManganese oreCopper oreCornQuartzTimberTin oreLead oreSilver oreZinc oreSugarcaneSugar beet

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Keep walking

Indium tin oxide 7 stations · 15 raw sources Asthma inhaler 6 stations · 16 raw sources Glass jar 5 stations · 10 raw sources Umbrella 8 stations · 19 raw sources Vulcanized rubber 6 stations · 7 raw sources Electric car battery 6 stations · 28 raw sources

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Sources

Cite this page: "How hard drives are made." Assembly Line, 2026-11-03. https://assemblyline.org/make/hard-drive

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