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Is A Kilobit 1,000 Or 1,024 Bits?: A Mathematical Debate Explained

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What is a kilobit equal to? The answer is 1,000 bits, but some people say it should really be 1,024.

The debate over how many bits are in a kilobit has popped up many places (including in our comments section today), with some people championing 1,000 and others 1,024. So what's the answer? Well, today, the answer is that a kilobit is 1,000 bits. But that wasn't always the case. It used to be 1,024. Why the change?


The initial number of 1,024 bits was arrived at by early computer scientists who routinely used binary measurements in their work. Specifying 2^10 was a little unwieldy, but adding a kilo prefix to bit was, if not exactly correct, close enough. And, at the time, the computer community was small enough that it was common knowledge that the kilo prefix came with a bit of a wink (to the tune of 24 extra bits) appended to it.

So what changed? All the rest of us showed up to the party — and then things got a little confusing. The National Institute of Standards and Technology explains:

That worked well enough for a decade or two because everybody who talked kilobytes knew that the term implied 1024 bytes. But, almost overnight a much more numerous "everybody" bought computers, and the trade computer professionals needed to talk to physicists and engineers and even to ordinary people, most of whom know that a kilometer is 1000 meters and a kilogram is 1000 grams.


But, just to make it even messier, different industries began to adopt different meanings for numerical prefixes depending on their own individual needs. And the problem wasn't just with the kilobit, the bigger data storage got, the bigger the problem became.

Consider the confusing case of the megabyte:

When discussing computer memory, most manufacturers use megabyte to mean 220 = 1 048 576 bytes, but the manufacturers of computer storage devices usually use the term to mean 1 000 000 bytes. Some designers of local area networks have used megabit per second to mean 1 048 576 bit/s, but all telecommunications engineers use it to mean 106 bit/s. And if two definitions of the megabyte are not enough, a third megabyte of 1 024 000 bytes is the megabyte used to format the familiar 90 mm (3 1/2 inch), "1.44 MB" diskette. The confusion is real, as is the potential for incompatibility in standards and in implemented systems

Faced with the problem, the NIST finally threw its hands up and decreed that they were setting up a standard meaning that would apply across the board: From here on, the kilobit would be 1,000 bits.

Fortunately for those who do their best work in base 2, however, there was a also a consolation prize at the end of all this: the kibibit, which would retain the original 1,024 bits designation.


Image: bittbox