Thursday, November 10, 2011

Hard drive sizes - why marketing should be shot

Have you ever bought a new hard drive for your computer, but after installation the drive isn't as large as the package claims? Well the short answer is because the marketing department at the hard drive company lied to you. Every manufacture does it, and there is some precedence for what they've done.

It all comes down to math. Computers operate in terms of binary, 1s and 0s. A single 1 or 0 is called a bit. They group 8 of these bits together and call it a "byte." A byte is the smallest representation of data that computers store. When talking about larger numbers typically use prefixes like Kilo, Mega, etc. A kilobyte (KB) is 1,024 bytes. 1024 might seem like an odd choice, but they use it because 2^10 equals 1,024. And since computers use binary this was the obvious choice.

So where does the precedence come in? Well 1,024 is fairly close to 1,000 and as far as the human brain is concerned, doing math with 1,000 is a lot easier than 1,024. So it became common practice to use 1,000 to represent kilobytes. The problem is, as sizes get larger, the error compounds itself. Check out the following table:

Size / Percent difference

Kilobyte / 2.4%
Megabyte / 4.9%
Gigabyte / 7.4%
Terabyte / 10.0%

As you can see the error increases with each increased size. So if you buy a brand new 4 terabyte hard drive, it can actually store only 3.6 terabytes, or 90% of the claimed value. Hopefully at some point hard drive manufactures will discontinue this lie and accurately label their products.

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