We store our digital lives on hard drives for the most part. This series of articles covers everything you want to know about hard drives, their care and best practices.

What is in a hard drive?

It’s been said that the beginning is a very good place to start. And when it comes to hard drives, what’s in a hard drive is that very good place. We have to understand how they’re made and what they do internally so that we can understand how to protect them from failure for as long as possible. So what’s in a hard drive? The first component is the spinning platter. The platter is where the data is stored. It’s written by the read-write head, and these two interact.

This video is from Hard Drive Management for Creative Pros by Kevin Ames

The platters

What happens is the spinning platter is running between 5400 RPM or 7200 RPM. That means, in a 7200-RPM drive, the edge of the platter is traveling at about 67 miles per hour. It’s been suggested by people that they just speed up the platter spin on the hard drive to be able to get a faster read-write. They said, “Well, why don’t they go to 20,000 RPMs?” Well, at that speed, the edge of the platter is hitting close to the speed of sound, which would tear the drive apart.

The read-write head

The read-write head moves across the platter and seeks out where each segment of data is written. The important thing to know here is that the data isn’t written as it would be on a record or a compact disc. It’s not written in a continuous form. It’s written in segments called blocks, and they’re scattered all over the platters. In the case of the drive, I’m going to show you the platters in, there are three different platters. And the read-write heads move between these, finding the data using the computer’s ability to sort things out, to get each segment, and then the computer puts them together into the coherent data that we’re used to seeing.

Inside a hard drive

Whether it’s a Word document, a movie, or a photograph, none of it exists in one contiguous form. It’s all a bunch of individual little sectors scattered across the platter and found by the read-write head guided by the computer. The next component is a circuit board that’s on the bottom of the hard drive. That works to control where the read-write head seeks physically on the platter to find each segment of data.
Finally, there are connectors on the end of the hard drive that connects it to the computer, to the external housing or however you have it attached to your computer. Let’s take a look and see what’s inside a hard drive. I’ve already taken the screws out of the top, so I’m just going to pull it off and set it aside. And you get an idea of the complexity here. There’s also a piece right here that covers up the head that I’ve removed for purposes of clarity.

What happens inside a hard drive

The head moves across the platen and seeks, throughout all three of these platters, data. And you can see, on the edge here, where the platters are. There’s three of them, and there are three heads that track across the platter as well. So that’s basically all that’s in a hard drive. There’s a circuit board here, with an integrated circuit, a little computer of its own, that actually tells the hard drive, that actually tells the head where to seek on the platters.


And then there are the connectors, and these are the connectors that attach the hard drive to the computer. So those are the four components of all hard drives, the spinning platters, and there could be more than three or less than three, depending on the amount of data it holds, the read-write heads, the circuit board, and the connector. That’s all there is to a hard drive. And yet, if you think of the tolerances that are going on and the speeds, it’s quite a remarkable feat of engineering and manufacturing.

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