Media Notes / Binary Prefix

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You bring home a brand new 1 terabyte storage drive to store your collection of whatever it is (Games, pictures, music, porn). After getting it up and running, formatting it, etc. you find out that your OS reports only 909 gigabytes. Wait, did the hard drive manufacturers shortchange you out of some 90 gigabytes of capacity? Did formatting really eat up all that space? Nope, it turns out this is a problem with what hard drive manufacturers say is a kilobyte, megabyte, gigabyte, etc. and what operating systems say, creating Unit Confusion. Both are, for all intents and purposes, correct, just measured on different scales.

Most memory manufacturers, except those that make RAM, say a kilobyte is 1,000 bytes, a megabyte 1,000,000 bytes, a gigabyte 1,000,000,000 bytes and so on. This is following the normal SI standard of naming quantities.

Operating systems, given the Binary Bits and Bytes nature of computers, measure this in powers of 2^10. So a kilobyte is 2^10, a megabyte is 2^20, a gigabyte 2^30, and so on. Turns out there are more bytes in a given order of magnitude than the SI method.

It wasn't until 1998 that the convention of how operating system of measures memory became standardized by the International Electrotechnical Commission (IEC), being called binary prefixes. It's the same as the SI prefix, but just replace the last two letters with "bi". Kilobyte becomes kibibyte, megabyte becomes mebibyte, and so on. But to make things worse, either way of naming is valid. So while a gibibyte is without a doubt 2^30 bytes, a gigabyte could still be 1,000,000,000 bytes or 2^30 bytes.

Most operating systems still use binary prefix scaling to measure the size, but annoyingly still use SI prefixes to report it. Mac OS X and some Linux distributions (notably Ubuntu) use SI scaling for both measuring and reporting.

Note that most network speeds default to using bits per second using SI scaling. File transfers are usually reported with how the OS reports sizes.

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