Kilobyte

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Multiple-byte units
Decimal
Value Metric
1000 kB kilobyte
10002 MB megabyte
10003 GB gigabyte
10004 TB terabyte
10005 PB petabyte
10006 EB exabyte
10007 ZB zettabyte
10008 YB yottabyte
10009 RB ronnabyte
100010 QB quettabyte
Binary
Value IEC Memory
1024 KiB kibibyte KB kilobyte
10242 MiB mebibyte MB megabyte
10243 GiB gibibyte GB gigabyte
10244 TiB tebibyte TB terabyte
10245 PiB pebibyte
10246 EiB exbibyte
10247 ZiB zebibyte
10248 YiB yobibyte
10249
102410
Orders of magnitude of data

The kilobyte is a multiple of the unit byte for digital information.

The International System of Units (SI) defines the prefix kilo as a multiplication factor of 1000 (103); therefore, one kilobyte is 1000 bytes. The internationally recommended unit symbol for the kilobyte is kB.

In some areas of information technology, particularly in reference to random-access memory capacity, kilobyte instead typically refers to 1024 (210) bytes. This arises from the prevalence of sizes that are powers of two in modern digital memory architectures, coupled with the coincidence that 210 differs from 103 by less than 2.5%. A kibibyte is 1024 bytes.

Definitions and usage

Decimal (1000 bytes)

In the International System of Units (SI) the metric prefix kilo means 1000 (103); therefore, one kilobyte is 1000 bytes. The unit symbol is kB.

This is the definition recommended by the International Electrotechnical Commission (IEC). This definition, and the related definitions of the prefixes mega (1000000), giga (1000000000), etc., are most commonly used for data transfer rates in computer networks, internal bus, hard drive and flash media transfer speeds, and for the capacities of most storage media, particularly hard disk drives, flash-based storage, and DVDs. It is also consistent with the other uses of the metric prefixes in computing, such as CPU clock speeds or measures of performance.

The international standard IEC 80000-13 uses the term "byte" to mean eight bits (1 B = 8 bit). Therefore, 1 kB = 8000 bit. One thousand kilobytes (1000 kB) is equal to one megabyte (1 MB), where 1 MB is one million bytes.

Binary (1024 bytes)

The term 'kilobyte' has traditionally been used to refer to 1024 bytes (210 B). The usage of the metric prefix kilo for binary multiples arose as a convenience, because 1024 is approximately 1000.

The binary interpretation of metric prefixes is still prominently used by the Microsoft Windows operating system. Binary interpretation is also used for random-access memory capacity, such as main memory and CPU cache size, due to the prevalent binary addressing of memory.

The binary meaning of the kilobyte for 1024 bytes typically uses the symbol KB, with an uppercase letter K. The B is sometimes omitted in informal use. For example, a processor with 65,536 bytes of cache memory might be said to have "64 K" of cache. In this convention, one thousand and twenty-four kilobytes (1024 KB) is equal to one megabyte (1 MB), where 1 MB is 10242 bytes.

In December 1998, the IEC addressed such multiple usages and definitions by creating prefixes such as kibi, mebi, gibi, etc., to unambiguously denote powers of 1024. Thus the kibibyte, symbol KiB, represents 210 bytes = 1024 bytes. These prefixes are now part of IEC 80000-13. The IEC further specified that the kilobyte should only be used to refer to 1000 bytes. The International System of Units restricts the use of the SI prefixes strictly to powers of 10.

Use of term

Data examples

"This is an example of a text which is exactly a kilobyte (kB) large. In this case, this text is 10^3 bytes long, but if you were to add 24 extra characters to this string, it would be 2^10 bytes long, which is used in some fields such as information technology. Each character in this string (which includes the quotation marks at the end, by the way) is exactly one byte long, which is 8 bits. The bit is the fundamental unit of information, which represents a single yes or no. So, one could measure the amount of information in a single letter with 5 bits (because 2^5 is 32, there are 26 letters in the English language), but because we also use other characters, like numbers, capital/lowercase letters, symbols (like {}$#*&%!`~), spaces, and more. In a computer's memory, these may be represented with some binary string, such as 01010100 (which represents the letter T), usually this is distinguished from one million ten thousand one hundred by appending '0b' to the front, like 0b01010100."

See also

References

  1. ^ a b c International Standard IEC 80000-13 Quantities and Units – Part 13: Information science and technology, International Electrotechnical Commission (2008).
  2. ^ Prefixes for Binary Multiples Archived 2007-08-08 at the Wayback Machine — The NIST Reference on Constants, Units, and Uncertainty
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