The kilobyte is a multiple of the unit
byte
The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable uni ...
for
digital information.
The
International System of Units (SI) defines the prefix ''
kilo'' as 1000 (10
3); per this definition, one kilobyte is 1000 bytes.
[International Standard IEC 80000-13 Quantities and Units – Part 13: Information science and technology, International Electrotechnical Commission (2008).] The internationally recommended unit symbol for the kilobyte is kB.
In some areas of
information technology
Information technology (IT) is the use of computers to create, process, store, retrieve, and exchange all kinds of data . and information. IT forms part of information and communications technology (ICT). An information technology syste ...
, particularly in reference to solid-state memory capacity, ''kilobyte'' instead typically refers to 1024 (2
10) bytes. This arises from the prevalence of sizes that are
powers of two
A power of two is a number of the form where is an integer, that is, the result of exponentiation with number two as the base and integer as the exponent.
In a context where only integers are considered, is restricted to non-negati ...
in modern digital memory architectures, coupled with the accident that 2
10 differs from 10
3 by less than 2.5%. A
kibibyte
The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable uni ...
is defined by Clause 4 of
IEC 80000-13 as 1024 bytes.
Definitions and usage
Base 10 (1000 bytes)
In the
International System of Units (SI) the prefix ''
kilo'' means 1000 (10
3); therefore, one kilobyte is 1000 bytes. The unit symbol is kB.
This is the definition recommended by the
International Electrotechnical Commission (IEC).
[Prefixes for Binary Multiples](_blank)
— The NIST Reference on Constants, Units, and Uncertainty
This definition, and the related definitions of the prefixes
mega (),
giga (), etc., are most commonly used for
data transfer rate Data rate and data transfer rate can refer to several related and overlapping concepts in communications networks:
Achieved rate
* Bit rate, the number of bits that are conveyed or processed per unit of time
** Data signaling rate or gross bit rate ...
s in
computer network
A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are ...
s, internal bus, hard drive and flash media transfer speeds, and for the capacities of most
storage media, particularly
hard drive
A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with mag ...
s,
flash-based storage, and
DVDs. It is also consistent with the other uses of the
SI prefixes in computing, such as
CPU clock speeds or
measures of performance.
The IEC 80000-13 standard 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.
Base 2 (1024 bytes)
The term 'kilobyte' has traditionally been used to refer to 1024 bytes (2
10 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
Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for ...
operating system.
Metric prefixes are also used for
random-access memory
Random-access memory (RAM; ) is a form of computer memory that can be read and changed in any order, typically used to store working data and machine code. A random-access memory device allows data items to be read or written in almost the ...
capacity, such as main memory and
CPU cache
A CPU cache is a hardware cache used by the central processing unit (CPU) of a computer to reduce the average cost (time or energy) to access data from the main memory. A cache is a smaller, faster memory, located closer to a processor core, whi ...
size, due to the prevalent
binary address
In computing, a physical address (also real address, or binary address), is a memory address that is represented in the form of a binary number on the address bus circuitry in order to enable the data bus to access a ''particular'' storage cell o ...
ing of memory.
The binary meaning of the kilobyte for 1024 bytes typically uses the symbol KB, with an uppercase letter ''K''. The ''B'' is often 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 1024
2 bytes.
In December 1998, the
IEC
The International Electrotechnical Commission (IEC; in French: ''Commission électrotechnique internationale'') is an international standards organization that prepares and publishes international standards for all electrical, electronic and r ...
addressed such multiple usages and definitions by creating prefixes such as kibi, mebi, gibi, etc., to unambiguously denote powers of 1024. Thus the
kibibyte
The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable uni ...
, symbol KiB, represents 2
10 bytes = 1024 bytes. These prefixes are now part of the
IEC 80000-13 standard. 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.
Examples
* The
Shugart SA-400 5-inch
floppy disk (1976) held 109,375 bytes unformatted, and was advertised as "110 Kbyte", using the 1000 convention. Likewise, the 8-inch
DEC RX01 floppy (1975) held 256,256 bytes formatted, and was advertised as "256k". On the other hand, the
Tandon
Tandon (or Tandan, Tanden, or Tondon) is a surname found among Hindu Khatris and Sikhs of Punjab, India. It is derived from a Khatri clan.
Notable people
Notable people include:
Activists
*Purushottam Das Tandon, ''Bharat Ratna'', Indian freed ...
5-inch
DD floppy format (1978) held 368,640 (which is 360×1024) bytes, but was advertised as "360 KB", following the 1024 convention.
* On modern systems, all versions of
Microsoft Windows
Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for ...
including the newest ()
Windows 10
Windows 10 is a major release of Microsoft's Windows NT operating system. It is the direct successor to Windows 8.1, which was released nearly two years earlier. It was released to manufacturing on July 15, 2015, and later to retail on ...
divide by 1024 and represent a 65,536-byte file as "64 KB".
Conversely,
Mac OS X Snow Leopard and newer represent this as 66 kB, rounding to the nearest 1000 bytes. File sizes are reported with decimal prefixes.
* the binary interpretation was still used in marketing and billing by some telecommunication companies, such as
Vodafone,
AT&T
AT&T Inc. is an American multinational telecommunications holding company headquartered at Whitacre Tower in Downtown Dallas, Texas. It is the world's largest telecommunications company by revenue and the third largest provider of mobile ...
,
Orange and
Telstra.
See also
*
History of the floppy disk
A floppy disk is a disk storage medium composed of a disk of thin and flexible magnetic storage medium encased in a rectangular plastic carrier. It is read and written using a floppy disk drive (FDD). Floppy disks were an almost universal data ...
*
Binary prefix
A binary prefix is a unit prefix for multiples of units. It is most often used in data processing, data transmission, and digital information, principally in association with the bit and the byte, to indicate multiplication by a power ...
*
Timeline of binary prefixes
*
*
*
References
*
{{Computer Storage Volumes
Units of information