Coming toTerms with Bytes

Computer terminology is becoming more precise: the International Electrotechnical Commission, which creates standards for electronic technologies, is adopting new prefixes to describe data values. The new term "kibibyte" will more accurately describe the number of bytes in a kilobyte -- rather than being 1,000, as could be inferred by the prefix "kilo," a kilobyte actually has 1,024 (2 to the 10th power) bytes. The metric prefixes currently employed -- kilo, mega, giga, etc. -- accumulate as a power of 10, rather than the binary system used in computer code. Thus, the Commission will use kibi, mebi, gibi, tebi , pebi and exbi to express exponentially increasing binary multiples (2 to the 10th power, 2 to the 20th power, etc.). "There was a need to straighten this out," says Barry Taylor of the National Institute of Standards and Technology.

(Science 12 Mar 99)


Get Ready for the kibi, mebi, gibi, tebi, pebi and exbi

Information technology is spinning off a lexicon of terms to describe new computer hardware, software and Internet services practically as fast as the latest modems. However, some of the new terms are just not precise enough. Take kilobytes, megabytes and gigabytes, for example. The kilo, mega and giga prefixes, borrowed from the International System of Units, the modern metric system, designate 1,000, 1 million and 1 billion respectively. Yet a kilobyte, as computer experts know, is actually 1,024 bytes, and a megabyte is really 1,048,576 bytes.

This discrepancy stems from the need to write electronic information in binary code, using only two digits, ones and zeros, while the metric system is based on 10 digits. To describe large numbers of bytes, programmers used the closest approximate metric prefixes available at the time. Now, the International Electrotechnical Commission, which writes international standards for electronic technologies, has adopted new prefixes to more accurately express the values of quantities used in information technology.

With significant input from the National Institute of Standards and Technology, the IEC adopted kibi (Ki), mebi (Mi), gibi (Gi), tebi (Ti), pebi (Pi) and exbi (Ei) to represent exponentially increasing binary multiples. A kibibyte, therefore, equals 2 to the 10th power, or 1,024 bytes. Likewise, a mebibyte equals 2 to the 20th power, or 1,048,576 bytes. The new prefixes for binary multiples, which parallel the metric prefixes, will increase precision in expressing electronic information.

(NIST TechBeat - March, 1999)


prefix abbreviation value value
kibi Ki 210 1,024
kilo k 103 1,000
mebi Mi 220 1,048,576
mega M 106 1,000,000
gibi Gi 230 1,073,741,824
giga G 109 1,000,000,000