nuts and bolts : #1

This week, thanks to youtube’s recommendations, I spent a good 20 minutes watching the various possible ways to destroy a hard disk drive. Anything from over-clocking the rotation speed and pouring tomato ketchup on the disk to smashing a disk at 7500rpm with a hammer was covered! Those poor things…

But, something good came out of wasting all that time. In one of the videos, I saw the movement of the read/write head. It moved extremely quickly with extremely high accuracy; I think it was around 25 times per second and each time to a different position, mind you. Now, THAT IS FAST!! This made me think about the type of inner workings for such quick and precise mechanisms. What I found out through further digging was nothing short of an “ingenious” adaptation of existing technology.

Imagine having to move an object tens of times a second and every move must be accurate at the micrometer level. A stepper motor (or really any other type of motor) cannot offer that speed and accuracy right? What else could solve this problem? Read on to find out!

Meet the humble speakers. This is an extremely simple but incredible piece technology we take for granted everyday. Mobile phones, ear phones, car audio systems, home theatre systems etc use speakers of varying sizes and power to satisfy our entertainment needs. For the amount of work they do, their working principle is un-believably simple.

On a very high level, it works like this: the audio is sent to the speaker as a signal with highs and lows. This “wave” affects a magnet’s poles which make a coil of wire attached to a diaphragm, suspended between the poles, vibrate rapidly according to the wave’s high and low points. This vibration pushes the air back and forth producing the sound.

This high frequency, rapid back and forth movement of the coil-diaphragm system is what we are interested in. So, why explain this mechanism when we were talking about a hard disk’s heads? Because this is exactly the same technology adapted to move the read/write heads too. Positions of the data to be written/read on the HDD are fed to the read/write head’s magnets instead of an audio wave. And similar to a speaker’s coil moving due to the wave, the read/write heads also move. Really ingenious!


I also read on to find out that it is not the read/write head’s need to move rapidly which limits the HDD’s speeds, but it is the disk material’s mechanical strength that is the limiting factor. Too high a speed and the material breaks under the enormous centrifugal forces.

Now, of what use is it to learn about this mechanism? Will it benefit us as designers? Absolutely! If you ever have a need to move objects rapidly but accuracy is of paramount importance, this mechanism could come in handy. I can’t guess where you might need it, but neither could the person who invented it have guessed that it would be used in HDDs. I can tell you this though; It is beneficial (highly!) to equip ourselves with knowledge of such mechanisms to become better, versatile designers.

Here’s to hoping you learnt something new today!


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