Spinning storage, c. 2000s–2020s
A sealed aluminium box that keeps data as tiny magnetic patterns on spinning, mirror-smooth disks. Heads on a swinging arm read and write them while riding on a film of air far thinner than a smoke particle. Star-head screws hold it shut, and once the lid is off in ordinary room air the drive is usually finished: this is a one-way trip.
The lid. It seals the inside against dust and carries the label. A gasket runs round its underside, and two of its screws reach right down into the spindle and the arm pivot to steady them.
Made of Stamped steel or aluminium sheet with a rubber gasket, a printed label and a small filtered breather hole.
The little hole marked "do not cover" lets the air pressure inside even out with the room, through a filter. Drives filled with helium have no such hole: they are sealed shut instead.
Est. cost to the maker $1–3
The top half of the motor that swings the arm: a curved neodymium magnet glued under a thick steel plate. A matching magnet stays below, and the arm's flat coil moves in the gap between them.
Made of Neodymium-iron-boron magnet, nickel-plated against rust, on a low-carbon steel plate that carries the magnetic field round.
It is called a voice-coil motor because it works like a loudspeaker: current in a coil sitting in a magnet's field gives a push. Here the push swings the heads across the disk in a few thousandths of a second.
Est. cost to the maker $1–3
The arm that carries the read-write heads, one for each disk surface, on springy steel arms. Behind the pivot sits a flat copper coil, and a flexible cable takes the signals to a tiny amplifier chip on the side.
Made of Aluminium arm block, stainless-steel suspensions, ceramic sliders with thin-film magnetic heads, a copper coil in plastic, a polyimide flex cable and a ball-bearing pivot.
When the disks spin, each slider lifts on a cushion of air and flies only a few nanometres above the surface. A fingerprint smudge is hundreds of times thicker.
Est. cost to the maker $6–15
A plastic ramp at the edge of the disks. When the drive stops, the arm swings out and a little tab at its tip slides up the ramp, lifting the heads clear before they can touch the surface.
Made of A slippery, hard-wearing engineering plastic, moulded to within hundredths of a millimetre.
Older drives landed their heads on a textured strip near the hub every time they stopped. Ramp loading avoids that contact, and it spread from laptop drives to desktop ones.
Est. cost to the maker $0.25–0.5
A small pad of filter cloth standing in the wind that the spinning disks whip round the inside. It catches any specks shaken loose inside the sealed drive.
Made of Electrostatically charged polymer fibre felt in a moulded plastic frame.
The disks act as a fan: at full speed they drag the air inside into a fast swirl, and the filter sits where that wind pushes stray particles through it.
Est. cost to the maker $0.25–0.5
A springy steel disc screwed to the top of the motor hub. It presses the platters and the spacer between them down so they spin as one solid block.
Made of Spring steel, stamped and dished, held by a ring of small star-head screws.
Platters must never shift on the hub: the tracks are only tens of nanometres wide, so even a tiny slip leaves the heads lost. Data-recovery labs move whole platter stacks with special tools for this reason.
Est. cost to the maker $0.25–0.5
Two disks, polished like mirrors and coated with a magnetic film. Every file on the drive is a pattern of tiny magnetised regions laid out in circular tracks on both faces of each disk.
Made of Aluminium-alloy (or glass) disks plated with nickel-phosphorus, sputtered with cobalt-alloy magnetic layers, a carbon overcoat and a film of lubricant one molecule-thin; a spacer ring between them.
At 7,200 rpm the outer rim of a 95 mm platter moves at about 36 metres per second, roughly 130 km/h, while the head above it flies a few nanometres away.
Est. cost to the maker $6–16
The backbone: a die-cast aluminium tub with a brushless motor built into its floor. The motor's hub is what the platters sit on. The lower voice-coil magnet and the arm's pivot post are fixed here too.
Made of Die-cast aluminium alloy, machined flat on top; a motor with copper windings, a magnetised ring and a fluid bearing holding a few drops of oil.
Modern spindle motors turn on fluid bearings, where the shaft rides on a thin film of oil instead of steel balls. They are quieter and wear more slowly than ball bearings.
Est. cost to the maker $5–12
The drive's own little computer, screwed under the base. It runs the firmware, drives the motor and the arm, turns the faint signals from the heads into data, and talks to the PC over SATA.
Made of A glass-fibre laminate with several copper layers, a controller chip with processors inside, cache memory, a motor driver, a flash chip with firmware, and SATA connectors.
Swapping in the board from an identical drive often fails: each drive keeps calibration data unique to its own heads and platters, partly in a chip on this board, so recovery engineers move that chip across.
Est. cost to the maker $5–12
Prices are rough ranges of what the manufacturer pays for each part, pieced together from published teardown and bill-of-materials estimates. They vary a lot between models, years and order sizes, and they leave out assembly, software, research, shipping and profit. The drawing shows a generic device, not any particular model.