The Mystery of the Missing Megabytes

Since I was bored tonight anyway, I figured I might as well take this opportunity to clarify one of the more weird and strange computer behaviors out there: The seemingly unexplainable loss of hard drive space, that seems to grow bigger and bigger, the larger your hard drive is.

It’s actually pretty easy to explain. You see, it all boils down to math. If you buy a 500GB hard drive, specifications and packaging will list it as a 500GB, with an asterisk next to it. That asterisk will, at the bottom of the web page or paper take you to a disclaimer that will tell you that the number “500GB” is based on the fact that there are five billion bytes of space on the hard drive. And that, right there, is your first clue.

Most people know that 1KB is 1,000 bytes. 1MB is 1,000KB, and 1GB is 1,000MB. 1,000 of 1,000 of 1,000, et cetera.

We know this because we humans think in a base of 10 when we do math. It might have something to do with that being the number of fingers we have, it might not. If you want to know why humans think the way they do, you’re reading the wrong blog… I don’t know, and I’m not sure I want to know.

Anyway, that base of ten is how we make bigger numbers. Ten tens are a hundred. Ten hundreds are a thousand, ten thousands are ten thousand, and so on. Now here’s the problem: Since they don’t have fingers, computers don’t think that way.

Computers think in binary, which means they think with a base of two when they do math. That’s right, 2. When a computer wants to get to 1,000 it takes two, and then two twos. Then two of those, and two of those, and so on, until it finds itself as close as it can get to 1,000. Here is the beginning of the problem: The closest they can get is 2^10, but that doesn’t come out at 1,000 even. It comes out 1,024.

So where does this leave us, when we have a drive with 500,000,000,000 bytes of storage space? It means that when your computer looks at that drive and sees the 500,000,000,000 bytes, it gets to the number of gigabytes by dividing with 1,024 instead of 1,000. When you divide by a larger number, you get a smaller end result, that is basic math.

So let’s do the math on our 500GB hard drive, shall we?

500GB = 500,000,000,000 Bytes, per manufacturer’s specifications.

500,000,000,000 Bytes / 1024 = 488,281,250 Kilobytes

488,281,250 Kilobytes / 1024 = 476,837 Megabytes

476,837 Megabytes / 1024 = 465 Gigabytes

Yes. Your 500,000,000,000 hard drive is in binary speak 465GB in capacity, before initialized, partitioned and formatted.

This is the official established industry standard for reporting storage space on hard drives and SSDs. Is it honest? I’d say so. Is it misleading? Only if you don’t know any of what I just typed. Is it going to change? No, it’s not.

Storage devices have been labeled and described in this way since the day they were invented, way back when, in Steve and Bill’s garage in the early 70’s when they still hadn’t begun hating each others’ guts. So don’t call tech support and scream about being lied to, and threaten a law suit.

Really. It irritates us.

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Filed under Everything Computers, General Geekness

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