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 unit ...
for
digital information
Digital data, in information theory and information systems, is information represented as a string of discrete symbols each of which can take on one of only a finite number of values from some alphabet, such as letters or digits. An example is ...
.
The
International System of Units
The International System of Units, known by the international abbreviation SI in all languages and sometimes pleonastically as the SI system, is the modern form of the metric system and the world's most widely used system of measurement. E ...
(SI) defines the prefix ''
kilo
KILO (94.3 FM broadcasting, FM, 94.3 KILO) is a radio station broadcasting in Colorado Springs, Colorado, Colorado Springs and Pueblo, Colorado, Pueblo, Colorado. It also streams online.
History
KLST and KPIK-FM
The 94.3 signal signed on th ...
'' 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 system (I ...
, 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-negative ...
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 unit ...
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
The International System of Units, known by the international abbreviation SI in all languages and sometimes pleonastically as the SI system, is the modern form of the metric system and the world's most widely used system of measurement. E ...
(SI) the prefix ''
kilo
KILO (94.3 FM broadcasting, FM, 94.3 KILO) is a radio station broadcasting in Colorado Springs, Colorado, Colorado Springs and Pueblo, Colorado, Pueblo, Colorado. It also streams online.
History
KLST and KPIK-FM
The 94.3 signal signed on th ...
'' 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
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 ...
(IEC).
[Prefixes for Binary Multiples](_blank)
— The NIST Reference on Constants, Units, and Uncertainty
This definition, and the related definitions of the prefixes
mega
Mega or MEGA may refer to:
Science
* mega-, a metric prefix denoting 106
* Mega (number), a certain very large integer in Steinhaus–Moser notation
* "mega-" a prefix meaning "large" that is used in taxonomy
* Gravity assist, for ''Moon-Eart ...
(),
giga
Giga ( or ) is a unit prefix in the metric system denoting a factor of a short-scale billion or long-scale milliard (109 or ). It has the symbol G.
''Giga'' is derived from the Greek word (''gígas''), meaning "giant". The ''Oxford English Dic ...
(), etc., are most commonly used for
data transfer rates 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
Data storage is the recording (storing) of information (data) in a storage medium. Handwriting, phonographic recording, magnetic tape, and optical discs are all examples of storage media. Biological molecules such as RNA and DNA are consi ...
, 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 magne ...
s,
flash
Flash, flashes, or FLASH may refer to:
Arts, entertainment, and media
Fictional aliases
* Flash (DC Comics character), several DC Comics superheroes with super speed:
** Flash (Barry Allen)
** Flash (Jay Garrick)
** Wally West, the first Kid ...
-based storage, and
DVD
The DVD (common abbreviation for Digital Video Disc or Digital Versatile Disc) is a digital optical disc data storage format. It was invented and developed in 1995 and first released on November 1, 1996, in Japan. The medium can store any kind ...
s. It is also consistent with the other uses of the
SI prefix
The International System of Units, known by the international abbreviation SI in all languages and sometimes pleonastically as the SI system, is the modern form of the metric system and the world's most widely used system of measurement. E ...
es in computing, such as
CPU clock speeds or
measures of performance.
The IEC 80000-13 standard uses the term 'byte' to mean eight
bit
The bit is the most basic unit of information in computing and digital communications. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represente ...
s (1 B = 8 bit). Therefore, 1 kB = 8000 bit. One thousand kilobytes (1000 kB) is equal to one
megabyte
The megabyte is a multiple of the unit byte for digital information. Its recommended unit symbol is MB. The unit prefix ''mega'' is a multiplier of (106) in the International System of Units (SI). Therefore, one megabyte is one million bytes o ...
(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 serv ...
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 (computing), data and machine code. A Random access, random-access memory device allows data items to b ...
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, which ...
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 unit ...
, 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
The International System of Units, known by the international abbreviation SI in all languages and sometimes pleonastically as the SI system, is the modern form of the metric system and the world's most widely used system of measurement. E ...
restricts the use of the SI prefixes strictly to powers of 10.
Examples
* The
Shugart SA-400 5-inch
floppy disk
A floppy disk or floppy diskette (casually referred to as a floppy, or a diskette) is an obsolescent type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined w ...
(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 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 serv ...
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 J ...
divide by 1024 and represent a 65,536-byte file as "64 KB".
Conversely,
Mac OS X Snow Leopard
Mac OS X Snow Leopard (version 10.6) is the seventh major release of macOS, Apple's desktop and server operating system for Macintosh computers.
Snow Leopard was publicly unveiled on June 8, 2009 at Apple’s Worldwide Developers Conference. ...
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
Vodafone Group Public limited company, plc () is a British Multinational corporation, multinational Telephone company, telecommunications company. Its registered office and Headquarters, global headquarters are in Newbury, Berkshire, England. It ...
,
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 tel ...
,
Orange
Orange most often refers to:
*Orange (fruit), the fruit of the tree species '' Citrus'' × ''sinensis''
** Orange blossom, its fragrant flower
*Orange (colour), from the color of an orange, occurs between red and yellow in the visible spectrum
* ...
and
Telstra
Telstra Group Limited is an Australian telecommunications company that builds and operates telecommunications networks and markets voice, mobile, internet access, pay television and other products and services. It is a member of the S&P/ASX 20 ...
.
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 fo ...
*
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 of& ...
*
Timeline of binary prefixes
This timeline of binary prefixes lists events in the history of the evolution, development, and use of units of measure for information, the bit and the byte, which are germane to the definition of the binary prefixes by the International Electrot ...
*
*
*
References
*
{{Computer Storage Volumes
Units of information