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IEC binary prefixes

Recently, I discovered that the International Electrotechnical Commission, at some point, standardised these new prefixes for binary values.

Some people will know that a kilobyte is 1,024 bytes (not 1,000). Then a megabyte is 1,024×1,024 bytes. But it doesn’t apply to all things computer: there are 1,000 bits to a kilobit and 1,000 hertz to a kilohertz.

And, interestingly, a 4.7 gigabyte DVD holds 4,700,000,000 bytes — using decimal. CDs use binary: 700 MB = 734,003,200 bytes. Floppy disks kind of use both: 1.44 MB = 1.44×1,024×1,000 = 1,474,560 bytes.

And hard drive manufacturers, in their marketing schemes, claim capacities in decimal prefixes. So that 120 GB hard drive I bought in January isn’t actually 120 GB. It turns out to be about 111 GB. Talk about cheating the customer.

So, the IEC made these new prefixes that I’ve never ever heard of before. Neither has my electronics teacher. Instead of kilo, mega, giga etc. you use kibi, mebi and gibi for binary prefixes: when you want "kilo" to be 1,024. Clearly they’ve had trouble standardising them properly, because no-one uses them.

Just imagine saying those prefixes:

– "How big’s your file?"
– "It’s about 24 kibibytes."

"Kibi" sounds a bit funny, don’t you think? And, might I say, remarkably close to "Gibi"…

– "That’s a small file. I’ve got a good 25 gibibytes free space here."
– "I said 24 gibibytes. Don’t you have ears?"
– "Tebi or kibi? Make up your mind."
– "Pebibytes!"
– "What? Even your hard drive can’t fit 23 pebibytes."
– "I said gibibytes. Now have you got 23 gibibytes free space?"

Anyone fancy using those in everyday language?

Related Links

  • Mathew’s Journal: A plea for sanity
  • Prefixes for binary multiples on IEC
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