Gigabyte

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This article is about the unit of measurement. For the computer hardware manufacturer, see Gigabyte Technology. For the cartoon character, see ReBoot. For the virus writer, see Gigabyte (virus writer).
Multiples of bytes
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
Binary
Value JEDEC IEC
1024 KB kilobyte KiB kibibyte
10242 MB megabyte MiB mebibyte
10243 GB gigabyte GiB gibibyte
10244 - - TiB tebibyte
10245 - - PiB pebibyte
10246 - - EiB exbibyte
10247 - - ZiB zebibyte
10248 - - YiB yobibyte
Orders of magnitude of data

The gigabyte (/ˈɡɪɡəbt/ GIG-ə-byt or /ˈɪɡəbt/[1]) is a multiple of the unit byte for digital information.

The prefix giga means 109 in the International System of Units (SI), therefore one gigabyte is 1000000000bytes. The unit symbol for the gigabyte is GB.

This definition is used in all contexts of science, engineering, business, and many areas of computing. However, historically, the term has also been used in some fields of computer science and information technology to denote the gibibyte, or 1073741824 (10243 or 230) bytes. For instance, the memory standards of JEDEC, a semiconductor trade and engineering society, define memory sizes in this way.

To eliminate the ambiguity, the International Electrotechnical Commission has implemented the binary prefixes, a standard of multiplier prefixes for quantities expressed in binary multiples. The standard is endorsed by all 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 usage. The JEDEC industry consortium continues to permit the IEEE 100 nomenclature of using the metric prefixes kilo, mega and giga in their binary interpretation for memory manufacturing designations, but have endorsed the binary prefixes.

Definition[edit]

This 2.5" hard drive can hold 500GB of data.

The term gigabyte is commonly used to mean either 10003 bytes or 10243 bytes. This originated as compromise technical jargon for the byte multiples that needed to be expressed by the powers of 2 but lacked a convenient name. As 1024 (210) is approximately 1000 (103), roughly corresponding to SI multiples, it was used for binary multiples as well.

In 1998 the International Electrotechnical Commission (IEC) published standards for binary prefixes, requiring that the gigabyte strictly denote 10003 bytes and gibibyte denote 10243 bytes. By the end of 2007, the IEC Standard had been adopted by the IEEE, EU, and NIST, and in 2009 it was incorporated in the International System of Quantities. Nevertheless, the term gigabyte continues to be widely used with the following two different meanings:

Base 10 definition[edit]

Base 2 definition[edit]

Consumer confusion[edit]

Since the early 2000s, disk drive manufacturers based most consumer hard drive capacities in certain size classes measured in decimal gigabytes. The exact capacity of a given drive model is close to the class designation. Most manufacturers of hard disk drives and flash-memory disk devices[3][4] define one gigabyte as 1000000000bytes, which is displayed on the packaging. Some operating systems now express hard drive capacity or file size using decimal multipliers (integer powers of 1000), while others, such as Microsoft Windows, still report size in gigabytes by dividing the total capacity in bytes by 1073741824 (230 bytes= 1 gibibyte), while still reporting the result with the symbol GB. This discrepancy causes confusion, as a disk with an advertised capacity of, for example, 400 GB (meaning 400000000000bytes) might be reported by the operating system as 372 GB, meaning 372 GiB. Other software, like Mac OS X 10.6[5] and some components of the Linux kernel[6] measure in decimal units. The JEDEC memory standards use the IEEE 100 nomenclatures which define a gigabyte as 1073741824bytes (or 230 bytes).[7]

The difference between units based on decimal and binary prefixes increases as a semi-logarithmic (linear-log) function—for example, the decimal 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 might be indicated variously as 300 GB, 279 GB or 279 GiB, depending on the operating system. As storage sizes increase and larger units are used, these differences become even more pronounced. Some legal challenges have been waged over this confusion such as a suit against Western Digital.[8][9] Western Digital settled the challenge and added explicit disclaimers to products that the usable capacity may differ from the advertised capacity.[9]

Because of its physical design, the capacity of modern computer random access memory devices, such as DIMM modules, is always a multiple of a power of 1024. It is thus convenient to use prefixes denoting powers of 1024, known as binary prefixes, in describing them. For example, a memory capacity of 1073741824bytes is conveniently expressed as 1 GiB rather than as 1.074 GB. The former specification is, however, almost always quoted as 1 GB when applied to random access memory.

Software allocates 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. For example, the manufacturer of a "300 GB" hard drive is claiming a capacity of 300000000000bytes, not 300x10243 (which would be 322122547200).

Examples of gigabyte-sized storage[edit]

  • One hour of SDTV video at 2.2 Mbit/s is approximately 1 GB.
  • Seven minutes of HDTV video at 19.39 Mbit/s is approximately 1 GB.
  • 114 minutes of uncompressed CD-quality audio at 1.4 Mbit/s is approximately 1 GB.
  • A DVD-R single layer can hold about 4.7 GB.
  • A dual-layered Blu-ray disc can hold about 50 GB.

See also[edit]

References[edit]

  1. ^ The prefix giga may be pronounced two ways. Gigabyte - Definition and More from the Free Merriam-Webster Dictionary
  2. ^ http://physics.nist.gov/cuu/Units/binary.html Prefixes for binary multiples
  3. ^ a b SanDisk USB Flash Drive "Note: 1 megabyte (MB) = 1 million bytes; 1 gigabyte (GB) = 1 billion bytes."
  4. ^ a b Storage Chart "Megabyte (MB) = 1,000,000 bytes; 1 Gigabyte (GB) = 1,000,000,000 bytes; 1TB = 1,000,000,000,000 bytes"
  5. ^ a b "How Mac OS X reports drive capacity". Apple Inc. 2009-08-27. Retrieved 2009-10-16. 
  6. ^ units(7) - Linux manual page
  7. ^ JEDEC Solid State Technology Association (December 2002). "Terms, Definitions, and Letter Symbols for Microcomputers, Microprocessors, and Memory Integrated Circuits". Jesd 100B.01. 
  8. ^ Baskin, Scott D. (2006-02-01). "Defendant Western Digital Corporation's Brief in Support of Plaintiff's Motion for Preliminary Approval". Orin Safier v. Western Digital Corporation. Western Digital Corporation. Retrieved 2009-03-30. 
  9. ^ a b Mook, Nate (2006-06-28). "Western Digital Settles Capacity Suit". betanews. Retrieved 2009-03-30. 

External links[edit]