Why is my new 200GB harddisk only 186GB in size?

Or, Marketing Lies 2006.

Actually, this one is easy to explain.

Technically, a kilobyte is 1024 bytes (i.e., 2 to the tenth power), which of course is close to 1000 and of course "kilo-" means 1000. But we computer types always like to count by 2's and powers of 2. 1024 makes much more sense to a computer. It's really a coincidence that the
numbers work out like this.

Similarly megabytes really means 2²⁰ bytes or 1,048,576 bytes, but of course it's much easier to say it's a million bytes.

A gigabyte is really 1,073,741,824 bytes, although we humans (and especially lower life forms like marketing types) like to think it's a billion bytes.

So when your harddrive claims to be 200GB but your computer only reports it as 186GB, they are both correct. The marketing people just take the version of "gigabyte" that is most convenient for their purposes, whereas your computer uses the "correct" definition from a computer science point of view. The computer science gigabyte is 7% bigger, which explains the discrepancy. Of course, if your hard drive claims to provide 200GB of storage, you can rest assured that you are getting 200,000,000,000 bytes (give or take, formatting the disk takes up some of the space). Of course, since the price per byte for harddrives has dropped by a factor of about 20,000 since I bought my first harddrive in 1989, I'm not too worried either way.

There have been two proposals to fix this confusion:

1. The first proposal is that we use a different prefix when referring to the "computer science" versions of kilobyte, megabyte, etc, since "kilo-" is universally accepted to mean "one thousand", "mega-" universally means "one million". The idea proposed is to contract the word "binary byte" with the Systeme Internationale numerical prefix, so that 1024 bytes is "KIlo BInary BYTES" or "kibibytes". This also gives us "mebibytes", "gibibytes", etc. This has not caught on for two reasons: First, it is hopelessly pedantic, and second, it makes the speaker sound like he has some kind of speech impediment.

2. The second proposal is something I am making at this moment. A very dangerous plague that affects many parts of the world, especially third world countries, is that of land mines. There are millions of land mines around the world just waiting for some innocent person, years or even decades after the war in which the mines were used, to walk across it and lose a limb or even his life. I propose that we create an international task force for defusing all land mines and that they can be very effective by employing a very long stick with a marketing person tied to the end. If you are one of those people who claim (as I actually do) to hold human life precious, you can at least take the less satisfying alternative of mocking marketing types whenever possible, or at least buying a Dilbert book where it is already done for your convenience.

If you feel ripped off by the marketing legalese that gives you 7% less disk space than you think you are getting, be glad you weren't buying backup tapes in the early 90's. I didn't discover until too late when they described the capacity of a backup tape, they would assume a compression ratio of 2:1, meaning when they claimed the tape stored 120MB, that meant it really stored 60MB, and they "assumed" that you would use compression. Needless to say, this was much more dishonest that the "gigabyte" controversy described above, especially given the fact that the stuff I was backing up was usually compressed to begin with. I don't know if they do that any more since I haven't bought a backup tape in over a decade, but I wouldn't be surprised if there had been a class action lawsuit.

There actually was a successful class action lawsuit over the size of computer monitors. When describing the size of a monitor, the monitor manufacturers would describe the diagonal size of the cathode ray tube, a good inch to inch and a half of which was not usable because it was inside the frame of the monitor. The class action suit resulted, like all such suits, in some lawyers getting millions of dollars, while those of us actually affected by the wrong-doing got an insultingly small amount of money, and only if we went through some laborious process that would cost 5 or 10 or 20 times as much, given the value of our time, to actually receive. But at the least the monitor makers stopped this particular instance of lying.