What is that sound my hard drive is making?

I remember the first time looked into the guts of a hard drive. It was an RL02 connected to a PDP 11/44. The thing was huge, over 2 feet wide with room for a single platter of shiny dark brown ferrous material. The 5 mega-byte disks were removable and each was stored in a white and blue plastic case. There was a shock sensor on the handle that changed colour if the thing was dropped so some dumb ape wouldn’t put a warped disk into the drive and forever wreck the heads.

The most impressive sound the drive made was the satisfying clunk the drive made when the heads were being retracted. Then, there was the whirling sound of the platter spinning up to speed that sounded just like a jet engine starting up. Finally, there was the swish-swish of the heads gracefully moving over the platter seeking that valuable data stored so perfectly on the disk.

A friend of mine was hired as a sysop for a large mainframe back in the early ’80s. One day, while making a backup from one drive to another, there was a head crash that trashed the current working set of data being backed up. Now, most backup procedures, back then, were on a rotation of three sets of data: oldest, previous and current. This was primarily because of the high cost of each disk pack and three is the minimum you need for a safe backup. You take the current set and back it up over the oldest set which leaves the previous set untouched. Then, the oldest becomes the current, the current becomes the previous and the previous becomes the oldest. Well that’s how it’s suppose to work in theory. Since there was a head crash, the oldest set was only half overwritten with the current set and therefore useless. So, he thought: no problem, just put in the previous backup and restore to the oldest set thus making that the new current set. However, the one thing you don’t do when a head crashes is try and use the drive. What you do is put a “broken” sign on the drive and wait for the repairman. You see, the heads are often totaled in a head crash and if you put another disk pack into the drive, it’s going to get trashed too. But, he put in the previous backup, the last good copy of the data, filling the broken drive and destroying that set as well. There it was: all three copies of the data were lost. Needless to say, he wasn’t a sysop for long. But, I bet that hard drive made some pretty impressive noises before he was through.

Nowadays hard drives are faster, smaller and a lot less fragile. All they seem to do is make an awful rattling sound as the data rushes to and from the heart of the drive. We take them for granted. Where’s the poetry; where’s the grace. I think that part of the beauty of a computer has been lost. There was a certain mystery in its ability to create a kind of music as it went about its duty IMHO.

The familiar tune of Superstition reverberated through my desk. The sound was scratchy, not a FM scratchy, but a vinyl scratchy. The frequency response was wrong, actually, it was almost non-existent. With trained hand I inched up the voltage of my bench supply, eyes flashing between its needle and where the sound was coming from. A black plastic arm with a small PCB on one end jolted back and forth, the amplitude of its movement slowly and steadily increasing, with it the volume of the sound.

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VCRs, CD and DVD players, computer storage drives, printers (including fax machines and photocopiers) and document scanners, among other places you may find them, contain stepper motors. Now, a feature of stepper motors that is critical to what's about to be discussed is that they are extremely responsive. A two-stroke chainsaw motor might take a good couple of seconds to jump 100 RPM in speed, but a stepper motor can do it in the order of milliseconds. "Why is this useful?" you might be asking. Well, we will now look at how a speaker works. Speakers produce sound by vibrating a medium, whether it be a paper cone or air directly. Ok, so what if an electric motor were able to be started and stopped at audible frequencies?

This is precisely what someone did with the Commodore 1541 floppy disk drive. A Hacker discovered how to send the 1541's head madly seeking with the right timing to produce musical notes. There are a number of ways to achieve this "singing drive" phenomenon, and they are basically divided into hardware and software. I'm going to refer to floppy disk drives a lot, but most of what I'm saying is just as applicable to other forms of rotating computer storage drives.

I shall look at software first. Probably the method that requires the least modification to any existing hardware or software is to generate specially fragmented flat files from MIDI files, or any audio file really. In order to make this work, one must be intimately acquainted with the workings of their intended target drive, and its timing more specifically. The frequency of MIDI notes can be mapped to the time it takes a storage device's head to cover X number of blocks on the storage medium. Armed with this information, files can be crafted and copied to a diskette that, when the drive attempts to read, will cause its head to furiously skip back and forth over the disk, looking for the pieces of the file. The high-speed constant reversing of direction of the stepper motor the head's arm is attached to results in "music".

A second software solution requires talking directly to the stepper motor controller at a low level. To facilitate this, custom drivers must be written. Again, this requires a pretty intimate understanding of your target device, not only mechanically, but also how it communicates with other devices and probably a pretty solid grounding in how your operating system works. Having on the fly control of the stepper motor is advantageous over just throwing odd files at the drive mainly because it means you can turn the thing into, effectively, a MIDI hardware synthesiser. Having a hardware synthesiser lets you plug in a MIDI-equipped musical instrument, keyboard probably, and do live performances with the disk drive making the sounds.

Now we get to hardware solutions. What is wrong with software? Firstly, suppose you don't have a computer CD-ROM drive, but a Discman, how are you going to talk to that? (Please don't tell me you rigged a 555 timer to the back and next buttons) There could be other reasons you can't get at the existing controller, maybe you pulled the drive from a skip, and it's not entirely serviceable. Or maybe you're Top Gear, playing with a Renault Formula 1 car engine, but I haven't had first hand experience with this one, so we'll leave it for now. You'll probably want to supply your own stepper controller at this point. A PIC or similar microcontroller can do Pulse Width Modulation for you, so they are useful for standalone systems. Anyone want to be the first to turn a PS/2 keyboard + PIC + floppy drive into a musical instrument and record an album? Whether you use the existing stepper driver or your own, remember that you're going to have to do some programming to make it do what you want.

And now here's a completely hardware solution, no programming required at all. No, this is not a tape deck, your line level audio will not do. But add an amplifier, and the speaker output of an audio system can be fed directly to the motor coils. This setup differs significantly from the previous ones in that it is not limited to MIDI notes, but will accept the output of a Walkman or whatever else you want to throw at it. It is also by far the loudest way to go. After all, even SCSI drives aren't that audible on stage.

My current setup is, as you might expect, a combination of the proposed solutions. Custom drivers for a USB-controlled ATA 3.5" floppy drive turn it into a MIDI output. However, a transistor amplifier in line with the stepper motor overvolts it enough to make a "more reasonable" amount of noise.

Hopefully if you've read this far, you haven't started modifying anything yet. To be clear, you will almost certainly destroy your floppy drive and any disks inserted in it. If there are any disk drives mounted in nearby drive bays, the vibration will possibly damage them too. Disk drives were never meant to play music. (If you find one that was designed specifically to play music and still read and write disks afterwards, I'd be interested to hear about it) Playing music places disk drives under extreme mechanical abuse. They may misalign and/or shake themselves to pieces. While shaking themselves to pieces, shards of metal may fall across electrical paths, causing short circuits. This, along with overheating the motor, presents a fire hazard. In other words, doing any of what I have just described is probably a really stupid idea. So if you damage anything, it wasn't my fault, 'kay?

That said, go forth and destroy floppy drives!