How is data stored?

In this section I'm going to explain how that little box holds almost all of the information on your computer. This part will go a little bit into the physical components that make up a hard drive. These are the actual mechanical parts that move and make those funny whirring and clicking noises.

Where is the data stored?

A hard drive (or hard disk drive) is the rectangular, box-like device. (duh.) Inside of this are platters, which are flat and round plate-like things. These platters are coated with a magnetic material which is very, very thin, and then a lubricating layer on top of that which is for protection from things getting on to the platter, whether they be the actual head touching the platter, or some kind of dust or something. The magnetic material stores magnetic patterns.

How the data is written and read back

To get these magnetic patterns on the platter, there are read/write heads, which are electromagnetic components that can write magnetic patterns, or read back ones that have already been written. The read/write heads are attached to actuators, which are arm-like things, which control the position of the read/write head in relation to the platter. Platters are mounted in the center through a hole, and are stacked on a central rod-like thing called a spindle. The spindle is attached to a motor, which turns the spindle consequently allows the platters to spin.

So the spindle causes the platters to spin, and the actuator moves the read/write heads to certain positions of the platter, where it will look for certain data that it was requested to find. The whole process is much more refined than my words here make it sound. There is a great deal of precision involved. The components have to deal with tolerances that are measured in microinches. Even with my summarized explanation here, I'm sure you all can see that there are a great many mechanical components involved in hard drive operation.

Now that's some crazy precision!

Take the read/write heads, for example. These things are the electromagnetic devices that do the actual reading and writing of data. They do this by having the write head convert an electric signal (given by the system) into a magnetic pattern, which is stored on the platter's magnetic media. Then, when this data is needed, the read head picked the magnetic pattern up and translates it back into an electric signal. This is not the amazing thing, though. The crazy part of it is how the read/write heads interact with the platters. There are usually 2 heads per platter, although this is not always the case. In most cases there is a head above the platter, and one below.

Now when the actual read or write operation occurs, the heads don't actually touch the platter to do the job. They are barely millionths (literally) of inches away from the platter. This is, as you can guess, incredibly precise. Here's how it's done. When the hard drive is not in operation, the heads actually rest on the platters. This is done using a spring-type device. Now when the drive powers up and the spindle causes the platters to spin, the spinning creates an airflow that lifts the heads up. Of course, this is all calculated to make sure everything works correctly, but it's still pretty amazing.

Don't rock the boat!

This precision and sensitivity calls for a little special handling of the hard drive. Basically you don't want to move the hard drive around too much, or shake it around. Before you call me a "master of the obvious", I tell you this because I've seen people take hard drives that may or may not have been working and shake them vigorously. Needless to say, they didn't work quite right after that little exercise session. When the drive gets shaken like that, or dropped, you may alter the placement and position of the heads. When this happens, you may get a head crash.

These terribly feared words are when the read/write head comes into contact with the platter, while the platter is spinning. This is pretty much an irreversible event. While hard drives are manufactured to take some shock insulation, you obviously should be a little careful if you are moving your computer around, taking it to your friend's place, etc.