Gigabyte
Encyclopedia
The gigabyte is a multiple of the unit byte
for digital information storage. The prefix
giga means 109 in the International System of Units
(SI), therefore 1 gigabyte is . The unit symbol for the gigabyte is GB or Gbyte, but not Gb (lower case b) which is typically used for the gigabit
.
Historically, the term has also been used in some fields of computer science and information technology to denote the gibibyte
, or (10243 or 230) bytes. The Institute of Electrical and Electronics Engineers
(IEEE) defined the unit accordingly for the use in power switchgear
. In 2000, however, IEEE adopted the International Electrotechnical Commission
(IEC) recommendation, which uses the metric prefix interpretation.
Today the usage of the unit gigabyte continues to depend on the context. When referring to disk storage capacities it usually means 109 bytes, often stated explicitly on the manufacturer's permanent sticker. This also applies to data transmission quantities over telecommunication circuits, as the telecommunications and computer networking industries have always used the SI prefixes with their standards-based meaning. When referring to RAM
sizes it most often (see binary prefix adoption) has a binary interpretation of 10243 bytes, i.e. as an alias for gibibyte
. File systems and software often list file sizes or free space in some mixture of SI units and binary units; they sometimes use SI prefixes to refer to binary interpretation – that is using a label of gigabyte or GB for a number computed in terms of gibibytes (GiB), continuing the confusion.
In order to address this the International Electrotechnical Commission
has been promoting the use of the term gibibyte
for the binary definition. This position is endorsed by other standards organizations including the IEEE, the International Committee for Weights and Measures
(CIPM) and the U.S. National Institute of Standards and Technology
(NIST), but the binary prefixes have seen limited acceptance. The JEDEC
industry consortium continues to recommend the IEEE 100 nomenclature of using the metric prefixes kilo, mega and giga in their binary interpretation for memory manufacturing designations.
reports size in gigabytes by dividing the total capacity in bytes by , while still reporting the result with the symbol "GB". This practice is a cause of confusion, as a hard disk with a manufacturer-rated capacity of 400 gigabytes might be reported by the operating system as only "372 GB", for instance. Other software, like Mac OS X 10.6 and some components of the Linux
kernel measure using the decimal units.
The JEDEC memory standards
uses the IEEE 100 nomenclatures which defines a gigabyte as (or 230 bytes).
The difference between units based on SI and binary prefixes increases as a semi-logarithmic (linear-log) function—for example, the SI kilobyte value is nearly 98% of the kibibyte, a megabyte
is under 96% of a mebibyte, and a gigabyte is just over 93% of a gibibyte value. This means that a 300 GB (279 GiB) hard disk is indicated only as 279 GB. As storage sizes increase and larger units are used, this difference becomes even more pronounced. Some legal challenges have been waged over this confusion such as a suit against Western Digital
. Western Digital settled the challenge and added explicit disclaimers to products that the usable capacity may differ from the advertised capacity.
Because of its physical design, computer memory capacity is a multiple of base 2, thus, memory size at the hardware level can always be factored by a power of two
. It is thus convenient to use binary units for non-disk memory devices at the hardware level, for example, in boards using DIMM
memory. That is, a memory capacity of , for example, is conveniently expressed as 1 GiB
as opposed to 1.074 GB. Software applications, however, allocate memory in varying degrees of granularity as needed to fulfill data structure requirements and binary multiples are usually not required. Other computer measurements, like storage
hardware size, data transfer rates, clock speeds, operations per second
, etc., do not depend on an inherent base, and are usually presented in decimal units.
Byte
The byte is a unit of digital information in computing and telecommunications that most commonly consists of eight bits. Historically, a byte was the number of bits used to encode a single character of text in a computer and for this reason it is the basic addressable element in many computer...
for digital information storage. The prefix
SI prefix
The International System of Units specifies a set of unit prefixes known as SI prefixes or metric prefixes. An SI prefix is a name that precedes a basic unit of measure to indicate a decadic multiple or fraction of the unit. Each prefix has a unique symbol that is prepended to the unit symbol...
giga means 109 in the International System of Units
International System of Units
The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...
(SI), therefore 1 gigabyte is . The unit symbol for the gigabyte is GB or Gbyte, but not Gb (lower case b) which is typically used for the gigabit
Gigabit
The gigabit is a multiple of the unit bit for digital information or computer storage. The prefix giga is defined in the International System of Units as a multiplier of 109 , and therefore...
.
Historically, the term has also been used in some fields of computer science and information technology to denote the gibibyte
Gibibyte
The gibibyte is a standards-based binary multiple of the byte, a unit of digital information storage. The gibibyte unit symbol is GiB....
, or (10243 or 230) bytes. The Institute of Electrical and Electronics Engineers
Institute of Electrical and Electronics Engineers
The Institute of Electrical and Electronics Engineers is a non-profit professional association headquartered in New York City that is dedicated to advancing technological innovation and excellence...
(IEEE) defined the unit accordingly for the use in power switchgear
Switchgear
The term switchgear, used in association with the electric power system, or grid, refers to the combination of electrical disconnects, fuses and/or circuit breakers used to isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be done and to clear faults...
. In 2000, however, IEEE adopted the International Electrotechnical Commission
International Electrotechnical Commission
The International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...
(IEC) recommendation, which uses the metric prefix interpretation.
Today the usage of the unit gigabyte continues to depend on the context. When referring to disk storage capacities it usually means 109 bytes, often stated explicitly on the manufacturer's permanent sticker. This also applies to data transmission quantities over telecommunication circuits, as the telecommunications and computer networking industries have always used the SI prefixes with their standards-based meaning. When referring to RAM
Ram
-Animals:*Ram, an uncastrated male sheep*Ram cichlid, a species of freshwater fish endemic to Colombia and Venezuela-Military:*Battering ram*Ramming, a military tactic in which one vehicle runs into another...
sizes it most often (see binary prefix adoption) has a binary interpretation of 10243 bytes, i.e. as an alias for gibibyte
Gibibyte
The gibibyte is a standards-based binary multiple of the byte, a unit of digital information storage. The gibibyte unit symbol is GiB....
. File systems and software often list file sizes or free space in some mixture of SI units and binary units; they sometimes use SI prefixes to refer to binary interpretation – that is using a label of gigabyte or GB for a number computed in terms of gibibytes (GiB), continuing the confusion.
In order to address this the International Electrotechnical Commission
International Electrotechnical Commission
The International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...
has been promoting the use of the term gibibyte
Gibibyte
The gibibyte is a standards-based binary multiple of the byte, a unit of digital information storage. The gibibyte unit symbol is GiB....
for the binary definition. This position is endorsed by other standards organizations including the IEEE, the International Committee for Weights and Measures
International Committee for Weights and Measures
The Interglobal Committee for Weights and Measures is the English name of the Comité international des poids et mesures . It consists of eighteen persons from Member States of the Metre Convention...
(CIPM) and the U.S. National Institute of Standards and Technology
National Institute of Standards and Technology
The National Institute of Standards and Technology , known between 1901 and 1988 as the National Bureau of Standards , is a measurement standards laboratory, otherwise known as a National Metrological Institute , which is a non-regulatory agency of the United States Department of Commerce...
(NIST), but the binary prefixes have seen limited acceptance. The JEDEC
JEDEC
The JEDEC Solid State Technology Association, formerly known as the Joint Electron Devices Engineering Council , is an independent semiconductor engineering trade organization and standardization body...
industry consortium continues to recommend the IEEE 100 nomenclature of using the metric prefixes kilo, mega and giga in their binary interpretation for memory manufacturing designations.
Consumer confusion
Since the early 2000s most consumer hard drive capacities are grouped in certain size classes measured in gigabytes. The exact capacity of a given drive is usually some number above or below the class designation. Although most manufacturers of hard disk drives and flash-memory disk devices define 1 gigabyte as , software like Microsoft WindowsMicrosoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
reports size in gigabytes by dividing the total capacity in bytes by , while still reporting the result with the symbol "GB". This practice is a cause of confusion, as a hard disk with a manufacturer-rated capacity of 400 gigabytes might be reported by the operating system as only "372 GB", for instance. Other software, like Mac OS X 10.6 and some components of the Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
kernel measure using the decimal units.
The JEDEC memory standards
JEDEC memory standards
The JEDEC memory standards are the specifications for semiconductor memory circuits and similar storage devices promulgated by the JEDEC Solid State Technology Association, a semiconductor trade and engineering standardization organization....
uses the IEEE 100 nomenclatures which defines a gigabyte as (or 230 bytes).
The difference between units based on SI and binary prefixes increases as a semi-logarithmic (linear-log) function—for example, the SI kilobyte value is nearly 98% of the kibibyte, a megabyte
Megabyte
The megabyte is a multiple of the unit byte for digital information storage or transmission with two different values depending on context: bytes generally for computer memory; and one million bytes generally for computer storage. The IEEE Standards Board has decided that "Mega will mean 1 000...
is under 96% of a mebibyte, and a gigabyte is just over 93% of a gibibyte value. This means that a 300 GB (279 GiB) hard disk is indicated only as 279 GB. As storage sizes increase and larger units are used, this difference becomes even more pronounced. Some legal challenges have been waged over this confusion such as a suit against Western Digital
Western Digital
Western Digital Corporation is one of the largest computer hard disk drive manufacturers in the world. It has a long history in the electronics industry as an integrated circuit maker and a storage products company. Western Digital was founded on April 23, 1970 by Alvin B...
. Western Digital settled the challenge and added explicit disclaimers to products that the usable capacity may differ from the advertised capacity.
Because of its physical design, computer memory capacity is a multiple of base 2, thus, memory size at the hardware level can always be factored by a power of two
Power of two
In mathematics, a power of two means a number of the form 2n where n is an integer, i.e. the result of exponentiation with as base the number two and as exponent the integer n....
. It is thus convenient to use binary units for non-disk memory devices at the hardware level, for example, in boards using DIMM
DIMM
A DIMM or dual in-line memory module, comprises a series of dynamic random-access memory integrated circuits. These modules are mounted on a printed circuit board and designed for use in personal computers, workstations and servers...
memory. That is, a memory capacity of , for example, is conveniently expressed as 1 GiB
Gibibyte
The gibibyte is a standards-based binary multiple of the byte, a unit of digital information storage. The gibibyte unit symbol is GiB....
as opposed to 1.074 GB. Software applications, however, allocate memory in varying degrees of granularity as needed to fulfill data structure requirements and binary multiples are usually not required. Other computer measurements, like storage
Computer storage
Computer data storage, often called storage or memory, refers to computer components and recording media that retain digital data. Data storage is one of the core functions and fundamental components of computers....
hardware size, data transfer rates, clock speeds, operations per second
FLOPS
In computing, FLOPS is a measure of a computer's performance, especially in fields of scientific calculations that make heavy use of floating-point calculations, similar to the older, simpler, instructions per second...
, etc., do not depend on an inherent base, and are usually presented in decimal units.
Examples of gigabyte-sized storage
- One hour of SDTVStandard-definition televisionSorete-definition television is a television system that uses a resolution that is not considered to be either enhanced-definition television or high-definition television . The term is usually used in reference to digital television, in particular when broadcasting at the same resolution as...
video at 2.2 Mbit/s is approximately 1 GB. - Seven minutes of HDTVHigh-definition televisionHigh-definition television is video that has resolution substantially higher than that of traditional television systems . HDTV has one or two million pixels per frame, roughly five times that of SD...
video at 19.39 Mbit/s is approximately 1 GB. - 114 minutes of uncompressed CD-qualityCompact DiscThe Compact Disc is an optical disc used to store digital data. It was originally developed to store and playback sound recordings exclusively, but later expanded to encompass data storage , write-once audio and data storage , rewritable media , Video Compact Discs , Super Video Compact Discs ,...
audio at 1.4 Mbit/s is approximately 1 GB. - A DVD-RDVD-RDVD-R is a DVD recordable format. A DVD-R typically has a storage capacity of 4.71 GB. Pioneer has also developed an 8.5 GB dual layer version, DVD-R DL, which appeared on the market in 2005....
can hold about 4.7 GB. - A dual-layered Blu-ray discBlu-ray DiscBlu-ray Disc is an optical disc storage medium designed to supersede the DVD format. The plastic disc is 120 mm in diameter and 1.2 mm thick, the same size as DVDs and CDs. Blu-ray Discs contain 25 GB per layer, with dual layer discs being the norm for feature-length video discs...
can hold about 50 GB. - A Universal Media DiscUniversal Media DiscThe Universal Media Disc is an optical disc medium developed by Sony for use on their PlayStation Portable handheld gaming and multimedia platform...
can hold about 0.9 GB of data. (1.8 GB on dual-layered discs.)
External links
- http://physics.nist.gov/cuu/Units/binary.html
- http://www.iec.ch/zone/si/si_bytes.htm
- http://www.quinion.com/words/turnsofphrase/tp-kib1.htm
- http://www.nist.gov/public_affairs/techbeat/tb9903.htm