Letters to PC World, December 2003

Letter of the Month: Understanding Hard-Drive Sizes

I've been reading about a group that's suing PC makers for deceptive advertising of hard-drive sizes ["PC Makers Sued Over Hard-Drive Storage," from MacCentral.com, the news site of PC World's sibling publication Macworld]. This case has no merit.

Hard-drive manufacturers usually determine the size of the drive based on the old metric standard, where kilo = 1000. So the notations are powers of ten (kilo, mega, giga). But this group seems to believe that kilo = 1024 (or 2¹⁰) and that PC makers are using deceptive notations to promote drive sizes. Not so. A kilobyte (KB) normally means 1000, but a kibibyte (KiB) = 1024, according to the International Electrotechnical Commission standard. Manufacturers are using the correct notation, as they are calculating the hard-drive size (unformatted) using the old standard (metric).

When a PC or operating system calculates a drive's capacity, the result will be a multiple of 1024 (1 kibibyte), but it uses metric notation such as gigabyte rather than gibibyte. So while capacity measurements may state x billion bytes (GB), actual formatted capacity will be less.

Aaron Lindsay, via the Internet