Gigabyte

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Gigabyte is a SI-multiple of the unit byte for digital information storage. Since the giga- prefix means 10⁹, gigabyte means 1,000,000,000 bytes (1000³, 10⁹). However, this term is also often used meaning 1,073,741,824 bytes (1024³, 2³⁰).

Originally the binary use of prefixes like kilo-, mega-, giga- was confined to contexts where the sizes naturally came in powers of two, like memory or disk sizes, so that no confusion was possible. Later, disks with arbitrary sizes became available, and great confusion ensued.

Today the usage of the word "gigabyte" is ambiguous: the value depends on the context. When referring to RAM sizes it traditionally has a binary interpretation of 1024³ bytes. Some operating systems also list file sizes in binary units. When referring to disk storage capacities and data transmission volume over telecommunication lines, it means 1000³ bytes.

In order to address this confusion, the International Electrotechnical Commission (IEC) has been promoting the use of the term "gibibyte" for the binary definition. This position is endorsed by other standards organizations including the Institute of Electrical and Electronics Engineers (IEEE), the International Committee for Weights and Measures (CPIM) and the National Institute of Standards and Technology (NIST) but has seen limited acceptance.

Gigabyte is commonly abbreviated GB or Gbyte (not to be confused with Gb, which is used for a gigabit). Gibibyte is abbreviated GiB.

[edit] Definition and usage

There are two different interpretations of gigabyte in general use:

• 1,000,000,000 bytes or 10⁹ bytes is the official definition, based on the metric system (SI) of prefixes for multiples. It is used in telecommunications for network speeds and traffic volume and by most computer storage manufacturers for capacities of hard disks and flash drives. Quote from Seagate: "For drive storage capacity, 1 gigabyte = 1,000,000,000 bytes (or one billion bytes).",^[1] Similar quotes are found on the websites and products of other storage manufacturers. The Linux kernel also uses this definition.
• 1,073,741,824 bytes, equal to 1024³, or 2³⁰ bytes is the interpretation commonly used for computer memory and often file sizes. Microsoft uses this definition to display hard drive sizes^[2]. Since 1999, the IEC has defined this quantity as gibibyte(abbreviated GiB) and most standards bodies now recommend this usage.

The IEC's recommendations are frequently ignored amongst computer professionals, and "gigabyte" is used colloquially to mean 1024³ bytes. The JEDEC Solid State Technology Association, another standards body, acknowledges the conflict by noting that in light of the existence of the IEC recommendations this usage is deprecated but, in recognition of the widespread colloquial usage, it continues to recognize the usage of 1024³ bytes solely in the context of semiconductor storage capacities.^[3]

[edit] Gigabytes vs. gigabits

In conventional modern usage, a byte is 8 bits. One gigabyte is equivalent to eight gigabits.

In computer networking the conventional SI units are followed. Manufacturers of networking equipment always use 1000-bit kilobits as their basic unit of measurement.

[edit] Consumer confusion

This section does not cite any references or sources. Please help improve this section by adding citations to reliable sources. Unverifiable material may be challenged and removed. (February 2009)

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 1,000,000,000 bytes, the computer operating systems used by most users usually calculate size in gigabytes by dividing the total capacity in bytes (whether it is disk capacity, file size, or system RAM) by 1,073,741,824. This distinction is a cause of confusion, as a hard disk with a manufacturer-rated capacity of 400 gigabytes may be reported by the operating system as only 372 GB large, depending on the type of report.

The difference between units based on SI and binary prefixes increases exponentially—for example, the SI kilobyte value is nearly 98% of the kibibyte, but 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 drive appears as only 279 GB large. As storage sizes increase and larger units are used, this difference becomes even more pronounced.

Some consumers feel short-changed when they discover the difference, and claim that manufacturers of drives and storage devices are using the decimal measurements in an intentionally misleading way to inflate their numbers. Several legal disputes have been waged over the confusion.

Due to its physical design, computer memory is addressed in multiples of base 2, thus, memory size can always be factored by a power of two (for instance, 384 MiB = 3×2²⁷ bytes). It is thus convenient to use binary units for non-disk memory devices at the hardware level (for example, in using DIMM memory boards). Most software application have no particular need to use or report memory in binary multiples and operating systems often use varying granularity when allocating it. Other computer measurements, like storage hardware size, data transfer rates, clock speeds, operations per second, etc., do not have an inherent base, and are usually presented in decimal units.

To further complicate matters, flash memory chips, which are often used in disk-like devices, are organized in multiples of 2, like random access memory (RAM), but retail flash memory products have available capacities specified by multiples of 10. Removable flash storage products contain file systems that make the devices behave like hard disks instead of RAM, yet it is called 'memory'. In operating systems like Windows Vista, flash memory can be used as disk cache (ReadyBoost), but it really is not RAM.

Aggravating the confusion is that in some countries where non-metric systems of units are still in use for many measurements, the correct definition of many common SI units and their multiples is not well known by the public.^{[citation needed]}.

Some settlements of legal challenges against vendors have included directions for manufacturers to use clearer information, e.g., by stating a hard disk's size in both GB and GiB units. However, JEDEC memory standards still use the IEEE 100 nomenclatures.

[edit] Gigabytes in use

• One hour of VHS quality mpeg4 encoded video is approximately 1 GByte.
• One hour of HDTV video is approximately 4.2 GBytes.
• A basic unix system installation uses less than 1 Gbyte.
• 1.7 hours of uncompressed CD-quality sound fits in 1 Gbyte.

[edit] See also

• Megabyte
• Terabyte
• Binary prefix
• JEDEC memory standards
• Orders of magnitude (data)

[edit] References

[edit] 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