Attention hard drive manufacturers! Most people believe that a kilobyte is 1,024 bytes!

Operating systems use a binary system to measure disk space, while hard drive manufacturers use a decimal system. The result - When you fit a 750GB drive to your PC and fire up your OS, you only see 698.5GB - a whopping 51.5GB short of what most people expect to see.

It seems that the hard drive maker Western Digital has caved in and will offer free software to some 1 million consumers in order to resolve a class-action lawsuit that alleged that hard drives sold stored less information than promised.  To resolve this class-action, Western Digital is to give away backup and recovery software to anyone who bought Western Digital hard drives between March 22, 2001, through February 15 2006 (if you bought a hard drive and want to claim what's due to you under this settlement, you must register your claim before July 16 at

The problem is one of standards that I've talked about for years and I think that Western Digital has been wise to avoid taking this issue to court.  Operating system makers like Microsoft and Apple use a binary system to measure kilobyte, megabytes and gigabytes.  Under this scheme, a kilobyte is made up of 1,024 (210) bytes, a megabyte is made up of 1,048,576 (220) bytes and a gigabyte made up of 1,073,741,824 (230) bytes.  Hard drive manufacturers on the other hand use the decimal system for calculating the number of bytes that go to make a kilobyte, megabyte and gigabyte - 1,000 (103), 1,000,000 (106) and 1,000,000,000 (109) respectively.  The upshot of all this is that for every gigabyte fitted as storage to a PC, when this is measured by Windows or Mac OS, the customer gets 74 megabytes less than they expect to see.  That doesn't sound like a lot, but if you scale it up, it becomes pretty noticeable.  For example, take the latest 750GB perpendicular drives.  When you buy one of these and hook it up to a PC and fire up your OS, you only see 698.5GB - that's a whopping 51.5GB short of what most people expect to see (that's equivalent to nearly 6 full-length DVD movies).

The confusion goes deeper than just hard drives.  While CD capacities are given in binary units, DVDs are measured in decimal units.

Now you might be wondering how come this is legal and how come there hasn't been a lawsuit long before this one.  Well, the problem is that the trick could well be legal because the prefix "kilo" is a recognized prefix which is shorthand for 103 or 1,000 under the SI standard.  Under the same standard "mega" is short for 106 or 1,000,000 and "giga" is short for 109 or 1,000,000,000.  The prefix for binary representations are different, where "kibi" represents 210, "mebi" represents 220 and "gibi" which represents 230.

So is this a case of conforming to standards (the SI standards) or is it just a trick?  The kilobyte  = 1,000 bytes dates back to serially accessed data (such as punch cards) and the first hard drives used the same format.  However, times have moved on a lot since punch cards and I feel it’s got to the point where is starts to feel more and more like a trick so maybe it's high time media manufacturers accepted that, in computing circles, the binary system has become the recognized standard and start labeling drives based on what the end user will see.  If they are concerned about the perceived drop in capacity then why not adopt a dual system - such as 750GB/698.5GiB. Otherwise I think more and more people are going to notice what they're missing and more lawsuits will follow.


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