The Inner World of the Hard Drive

By Loyd Case  |  Posted 2005-03-18 Print this article Print

Holy microscopic elements, Batman! Loyd dissects an ordinary hard drive and finds a tiny universe of components moving with unbelievable speed.

When people think of personal computers, they almost always think of the CPU, or memory, or even graphics chips. They often forget that inside a PC is a purely mechanical device that spins at up to 15,000 revolutions per minute. In a more standard desktop hard drive, which spins at a tamer 7,200 RPM, a point close to the outer track is moving at roughly 48 miles per hour. In a typical working day, that means the outer edge of your hard drive has traveled 384 miles.

But thats not the most amazing part. Each hard drive consists of one or more platters, called the substrate, typically made from very thin glass. Were not talking window glass here, but a precisely formulated glass or glass composite, which is highly polished and coated with a thin layer of magnetic material. The drive can record data on both sides of a platter by orienting magnetic domains within the material. One direction represents a digital 1, the other a 0. In modern high-capacity drives, Magnetic domain orientation is often vertical (pointing up or down).

The key to all this is the heads. While the material making up the platters and magnetic media is certainly important, the read and write functions are handled by the heads, which fly barely one micron above the platter surface. To put this in context, a human hair is roughly 200 microns in diameter. Keep in mind that the platter is moving beneath the head at 7,200 RPM—thats like flying a jet about a foot above the ground. Since drives today can have up to five platters, each with two recording surfaces, you can have as many as ten heads, each hovering over its own surface. Multiple heads are part of a single mechanism, though; they cannot move independently. This makes them easier to control.
Read the rest of this article on ExtremeTech.
Loyd Case came to computing by way of physical chemistry. He began modestly on a DEC PDP-11 by learning the intricacies of the TROFF text formatter while working on his master's thesis. After a brief, painful stint as an analytical chemist, he took over a laboratory network at Lockheed in the early 80's and never looked back. His first 'real' computer was an HP 1000 RTE-6/VM system.

In 1988, he figured out that building his own PC was vastly more interesting than buying off-the-shelf systems ad he ditched his aging Compaq portable. The Sony 3.5-inch floppy drive from his first homebrew rig is still running today. Since then, he's done some programming, been a systems engineer for Hewlett-Packard, worked in technical marketing in the workstation biz, and even dabbled in 3-D modeling and Web design during the Web's early years.

Loyd was also bitten by the writing bug at a very early age, and even has dim memories of reading his creative efforts to his third grade class. Later, he wrote for various user group magazines, culminating in a near-career ending incident at his employer when a humor-impaired senior manager took exception at one of his more flippant efforts. In 1994, Loyd took on the task of writing the first roundup of PC graphics cards for Computer Gaming World -- the first ever written specifically for computer gamers. A year later, Mike Weksler, then tech editor at Computer Gaming World, twisted his arm and forced him to start writing CGW's tech column. The gaming world -- and Loyd -- has never quite recovered despite repeated efforts to find a normal job. Now he's busy with the whole fatherhood thing, working hard to turn his two daughters into avid gamers. When he doesn't have his head buried inside a PC, he dabbles in downhill skiing, military history and home theater.

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