EM education | deconstructing hard drives

What is Electromagnetic Education?

– deconstructing the computer hard drive –

THE computer hard drive is an object often referred to in regards to the value of taking one apart. This can also be said for floppy drives and ball-driven mice, yet the hard drive is also an aesthetic wonderland. And what follows is a brief attempt to convey some of the wonder that can be found in disassembling such a complex device, to learn more about it through further contemplation...

Actuator arm with circuit board from computer hard disk unit.
©-free. photograph by electronetwork.org, 2004.

IN taking apart a hard drive the key physical intersection appears to be the interaction between the actuator arm, and the rotating magnetic platters. It is at the tip of the robotic arm that computer data is read and written by way of its electromagnetic head.

Rare-Earth magnets inside protective enclosure. Magnetic fields
are very strong inside, very weak outside the enclosure.
©-free. photograph by electronetwork.org, 2004.

CIRCUITRY controls the actual arm and its tip, which moves back and forth inside a special enclosure for a rare-earth magnet interacting with the actuator arm at its base, which is wound with wire in close proximity to very strong, controlled magnetic fields.

Wires at the base of the actuator arm, with movement directed by the
control of strong magnetic fields by way of electromagnetic properties.
Note: the single wire from the wound wire at the base with the small side
circuit, which links then links to the main circuitry by plastic wire strip.
©-free, photograph by electronetwork.org, 2004.

THE circuit board that connects the computer with the hard drive enables the complex reading and writing of binary data at very high-speed. Hard disk drives are often referred to by specifications of both size and speed, such as 7,200 rpm (rotations per minute) of the magnetic platters, and the amount of data these platters are able to hold (20 gigabytes, for example, or roughly 13,000 floppy disks of information). The 'sound' one hears when a hard drive is performing its work may be related to the actuator arm moving back and forth across the moving platter, a type of choreography between the systems involved.

Hard disk platters for computer storage, actuator arm, and chip.
©-free, photograph by electronetwork.org, 2004.

THE chip or integrated circuit (IC) on the circuit board of this specific actuator arm was previously erroneously reported to be the Cirrus Logic CS5101A, though it was subsequently found out to be in error. The actual chip is the Cherry Semiconductor CS510A (pictured below) whose datasheet cannot be located, at present, online, to further determine its functioning.

Cherry Semiconductor, CS510A integrated circuit.
Educational fair-use, electronetwork.org 2004

(WHILE a chip schematic is currently not available to explore its functioning, a 'semiconductor logos' site was discovered that can help in correctly identifying the semiconductor company markings on a chip, to search for further information.)

IT is interesting to note that 'digital media', at the level of writing 'digital' bits onto a hard disk platter, still involves an analog component in the circuitry, to make such simplicity possible. Through some complex conversion of analog-digital signals, back and forth, electrical current carries digital information while precisely moving the actuator arm over the hard disk platters to read and write binary data.

TIPS at the end of the actuator arms, controlled by these chips, are able to be moved at high-speed, back and forth across the hard drive platters, to read-write data. At the tip of the actuator arms are a seemingly simple set of coiled wires around what appear to be felt pads, of which an electromagnetic field most likely is used to send current from one wire to the other, with the hard disk platter held delicately in-between the soft pads. In this case, two sets of actuator tips correspond to two layered platters for binary data storage.

Representation of magnetic data written to and read from sectors on a
hard disk storage platter in binary (North-South/South-North) format, with
unformatted sectors. ©-free, illustration by electronetwork.org, 2004.

IN this way a bit of information could be flipped as if a miniature bar magnet on the platter, moving it from a North-South orientation (0) to a South-North orientation (1) and thus changing the properties of the disk through such electromagnetic interactions. The actual process of reading and writing data would appear a simpler process than what is needed to direct and interpret this physical interaction via highly complex integrated circuitry.

HARD DRIVES are well-worth deconstructing and offer many ways to approach learning more about electronics by taking them apart. As artifacts they are incredibly interesting in their design, and rich in aesthetics. The magnets found inside are very powerful and should be handled with caution, the best idea is to leave them in their enclosure unless one knows how to safely extract them from their casing (without shattering them in the process). As with all things electronic, after taking a device apart, be sure to clean the circuitry and other things that are dismantled, as some contain lead and other chemicals that can burn the skin and eyes. Yet, as a project it is worthwhile to explore this device and in its design a major electronic component becomes a coherent whole, and while the physical and kinetic actions become more tangible, the importance of the integrated circuit to make it all work is all the more miraculous. (bc 9.10.2004)

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