In this lesson, I want to give you an easily understood explanation of a computer concept which is confusing to people pretty frequently. First, I’ll explain a couple of easy computer terms so you understand what you need to get the most out of this article.

I’m going to also explain why there seems to be a discrepancy between the size of a computer’s hard disk when you order it, or what’s on the label on your computer, and how much space is available on it, when you’re there looking at what it says on the computer screen, why it seems to not be as big.

First, allow me to define a couple of computer terms. These two terms are “erase” and “format.” Both of the terms essentially mean the same thing, so you can use them interchangeably.

A hard disk drive is the part of the computer which actually contains everything, your documents, pictures, music and the critical system files of a computer itself, that might be Windows or Mac OS X or anything else. In most cases, everything that’s saved on the computer is going to be kept on the hard disk.

Hard disks have been measured for some time in gigabytes and are now well on their way into the terabyte range, which is one order of magnitude up from a gigabyte.

A byte is essentially the smallest unit of measurement for computers (only bits are smaller than bytes).  A kilobyte is approximately 1,000 bytes. A megabyte is right around 1,000,000 bytes. A gigabyte is just about 1 billion bytes. A terabyte is basically 1 trillion bytes. It’s going to go far beyond that but not for a few more years, so forget about that for the time being.

Let’s say you have a machine which is a couple of years old. You may think you have a specific sized drive based on the label on the computer, or the specs on the sheet of paper that you got when you bought the machine.

So if you want to find out how big the drive is. When using a Macintosh, you can do this by clicking once on the the drive icon on your desktop, then clicking on the File menu and going to “Get Info.” That will tell you the size or capacity of the drive.

On a Windows computer, you double-click the Computer icon and click once on the hard drive. It will generally say what the size of the drive is on the left-hand side of the window.

If you find seeing something done is easier than reading the steps, I suggest Windows how to or Mac OSX how to training, but specifically video lessons so you can actually see the steps.

Once you see how big the drive is, it’s going to show up as less than what you think.

This is because of what happens when the drive is first set up for use. “Erasing” or “formatting” is preparing the drive ready for use. Before this happens, the drive is kind of like the foundation of a house before the house is built.

It’s not possible to live a house pad since there are no walls or roof. So that’s what happens when you setup a hard disk. You “partition” and format it. Maybe you’ve heard the word partition as one of those little dividers which divides one part of a room from another. A partition is basically the same thing.

When a person partition and format a hard drive, or erasing it, whichever term you prefer, what you’re doing is essentially raising the walls. You begin with the house pad, and then you put up the walls and the roof and you prepare it for use. Until you do that, a person can’t live in it.

For much the same reason, if you have a hard drive that’s not setup, you can’t store anything onto it because there are no walls or roof.

If you think about erasing or formatting a drive, that is, preparing it to be used, as being like putting a house on of a house pad, you might already start to guess why a hard drive’s size ends up seeming to be smaller.

It’s almost like you’ve lost space when you format it, compared to what the drive says it is if you look at the actual physical drive label, the box it came in or on the outside of the computer that came with that drive installed in it. It will say a larger size than you seem to have when you’re checking the drive’s size after it has been partitioned and formatted.

So if you begin with a house pad that is a thousand square feet, after you build the walls, you no longer have a thousand square feet left, not in practical, floor space. You have some of that space taken up by the walls.

Essentially speaking, that’s what happens when you format a disk. It gets partitioned and formatted and ready to use. In that process, that space is lost. You’ll probably find it’s a pretty good way to think about it, and it helps people understand.

Hopefully that makes sense and clears up a little bit of a mystery. Many of my clients have asked me about that — this is the way I explain it, and it seems to make sense to them. I hope it makes some sense to you, too.