I recently got an email from my friend Preston, who had this question:

“I’m wondering why, when you get a new hard drive, you don’t get the full amount of space that it says on the box? When I got my PC a few years ago, it said I had that 500 GB hard drive, but when I look at the drive, it only says I have 465 GB.”

So what do you have to say, hard drive manufacturers? Is this some kind of scam on the computer users of the world?

Not a scam. There’s a legitimate explanation for this. Actually there are a few reasons why this happens.

In case you’re not familiar with this, here’s what Preston is talking about. Your computer has a primary hard drive, and it was built to store a certain amount of data. The data is measure in either gigabytes or terabytes (1000 GB is virtually equal to 1 TB). Common sizes of hard drives these days are 500 GB, 750GB, 1TB, 2TB and sometimes even larger.

For example, the primary drive in my main computer is 2 terabytes. If I pulled the drive physically out of the computer, you would see right on the label that it says it’s a 2 TB drive. But if I check it while it’s in the computer (you can do this by holding down the Windows key, and tapping the letter E), it shows a different capacity:

That’s telling me I still have 1.5 TB of free space, but it says that the total overall space on the drive is only 1.81 TB. Why would it say that, if it’s supposed to be a 2 TB drive? There are a few reasons for this.

First, there could be a hidden partition on the drive. The most common type of hidden partition on a hard drive is a recovery partition. That partition contains the files and folders that would be used if Windows got messed up and needed to be reinstalled.

You know how when you first boot up your computer and for a few seconds you see on the screen that it’s telling you to hit F10 or some other key for “Recovery Options”? That what that hidden partition would be used for. Not all computers have this – it really depends on the manufacturer. And why do they hide that partition? So we computer users don’t mess with it and screw it up! But it still uses some of the space on your hard drive even though you can’t see it normally.

Second, there is a function in Windows that uses some space. That function is called System Restore. You’ve probably heard of it. This is where you can take your computer back to the state it was in on a particular date in the past, in order to fix some kind of problem that has come up more recently. It’s a handy thing to have in certain situations, but it can use up a good bit of space. Even just storing a single “past date” hard drive system state can be substantial – and if you check your System Restore window, you could find that you have 5 or 10 of them stored!

The third reason is the file system of the hard drive itself. The data on your hard drive needs to be stored in an organized manner, and it doesn’t do that on its own. There has to be a system to organize all those bits and bytes. And that system takes up a bit of space on its own.

Think of a physical file cabinet, like the one you might have in your office. That file cabinet might have a certain amount of space inside. But can you really use 100% of that space to store your files and folders? Nope. You will need something to hold your folders in place. Usually you start with a frame like this:

That takes up a small amount of space on its own. But then you also need the things that hang from that wire framework:

Then after you have that all set up, NOW you can start filing away your manila folders with your important papers. Granted, the frame and hanging files don’t take up a LOT of space, but they do take up SOME space – meaning you don’t really get to use 100% of the space inside that file cabinet for storage of your stuff.

So when you see that your 500 GB hard drive only has 465 GB of usable space, don’t worry, because it’s normal.

The real scammers? Cereal manufacturers!