Everything about Giga-byte totally explained
A
gigabyte (derived from the
SI prefix giga-) is a unit of
information or
computer storage meaning either exactly 1 billion
bytes (1000
3, or 10
9) or approximately 1.07 billion bytes (1024
3, or 2
30).
The usage of the word "gigabyte" is ambiguous, depending on the context. When referring to
RAM sizes and file sizes, it
traditionally has a binary definition, of 1024
3 bytes. For other uses, it means exactly 1000
3 bytes. In order to address this confusion, currently the
International Electrotechnical Commission (IEC) promotes 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).
It is commonly abbreviated
GB or
Gbyte (not to be confused with Gb, which is used for a
gigabit).
Definition
There are two different definitions of gigabyte in general use:
- 1,000,000,000 bytes or 109 bytes is the decimal definition, used in telecommunications (such as network speeds) and most computer storage manufacturers (such as hard disks and flash drives). This usage is compatible with SI. Quote from Seagate: "For drive storage capacity, 1 gigabyte = 1,000,000,000 bytes (or one billion bytes).", Similar quotes are found on the websites of other storage manufacturers.
- 1,073,741,824 bytes, equal to 10243, or 230 bytes. This is the definition commonly used for computer memory and file sizes. Microsoft uses this definition to display hard drive sizes, as do most other operating systems and programs by default. By this definition, there are 1,0243, or 1024×1024×1024 bytes in a gigabyte. (This is equivalent to 1,024 megabytes, where one megabyte is 1,048,576 bytes or 220 bytes.) Since 1999, the IEC recommends that this unit should instead be called a gibibyte (abbreviated GiB). Although there's little other usage of the term "gigabyte" apart from referring to memory, file sizes, or storage capacity, the IEC's recommendations are frequently ignored amongst computer professionals, and "gigabyte" is used colloquially to mean 10243 bytes. The standard body JEDEC Solid State Technology Association acknowledges the conflict and the existence of the IEC recommendations but, in recognition of the widespread colloquial usage, continues to recognize the definition of 10243 bytes.
Gigabytes vs. gigabits
In conventional modern usage, a byte is 8 bits. One gigabyte is equivalent to eight gigabits.
In computer networking, however, the conventional SI units are followed. Manufacturers of networking equipment always use 1000-bit kilobits as their basic unit of measurement.
| |
Abbreviation |
No. of bytes |
Usage |
| gigabytes | GB (Note: uppercase "B") |
10003 |
Computer storage (for example, 500 GB hard disk)
|
| gigabytes | GB (Note: uppercase "B") |
10243 |
Computer memory (for example, 4 GB RAM)
|
| gibibytes | GiB (Note: uppercase "B") |
10243 |
Computer storage (for example, 34 GiB file)
|
| gigabit | Gbit or Gb |
125*10002 |
Network throughput (eg 1 Gbit/s data transfer rate)
|
Consumer confusion
As of 2007, most consumer
hard drives are defined by their gigabyte-range capacities. The true capacity is usually some number above or below the class designation. Although most manufacturers of hard disks and Flash disks define 1 gigabyte as 1,000,000,000 bytes, the computer operating systems used by most users usually calculate a gigabyte by dividing the bytes (whether it's 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 have its capacity reported by the operating system as only 372 GB, depending on the type of report.
The difference between units based on SI and binary prefixes increases exponentially — in other words, an SI kilobyte is nearly 98% as much as a kibibyte, but a megabyte is under 96% as much as a mebibyte, and a gigabyte is just over 93% as much as a gibibyte. This means that a 500 GB hard disk drive would appear as "465 GB". As storage sizes get larger and higher units are used, this difference will become more pronounced.
Note that computer memory is addressed in
base 2, due to its design, so memory size is always a
power of two (or some closely related quantity, for instance 384 MiB = 3×2
27 bytes). It is thus convenient to work in binary units for
RAM at the hardware level (for example, in using
DIMM memory units). RAM memory size as seen by application software has no consistent bias towards power of two units, as the operating system will allocate memory in other granularities. Other computer measurements, like
storage hardware size,
data transfer rates,
clock speeds,
operations per second, etc., don't have an inherent
base, and are usually presented in decimal units.
An example, take a hard drive that can store exactly 250 or 250 billion bytes after formatting. Generally,
operating systems calculate disk and file sizes using
binary numbers, so this 250 GB drive would be reported as "232.83 GB". The result is that there's a significant discrepancy between what the consumer believes they've purchased and what their operating system says they have.
Some consumers feel short-changed when they discover the difference, and claim that manufacturers of drives and data transfer devices are using the decimal measurements in an intentionally misleading way to inflate their numbers. Several legal disputes have been waged over the confusion.
See Binary prefix — Legal disputes.
To further complicate matters,
flash memory chips are organized in multiples of 2, 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's called 'memory'. In operating systems like
Windows Vista, flash memory can indeed be treated like RAM.
The basis of the problem is that the official definition of the SI units isn't well known, and some legal settlements include directions for manufacturers to use clearer info, for example by stating a hard disk's size in both GB and GiB. However,
JEDEC memory standards still uses the IEEE 100 nomenclatures.
Gigabytes in use
The human genome contains 0.791175 GB of data (the 3.1647 base pairs(External Link
) represented as 2-bits).
A DVD-5 format disc is specified as capable of storing 4.7 gigabytes (4,700,000,000 bytes), or roughly 4.38 gibibytes. A DVD-9 is capable of storing 8.5 gigabytes, or roughly 7.91 gibibytes.
One gigabyte can hold over 1000 novels (uncompressed at 100,000 words per novel).
One gigabyte is roughly equal to 17 hours of MP3 music at 128 kbit/s (1,0003 / 128 / 1000 * 8 / 3600 = 17.36).
One gigabyte is roughly equivalent to 12 hours of Flash Video (at 450x370).
All 6th generation and 7th generation game consoles have game discs that are around 1 GB or more: Dreamcast (GD-ROM - 1.2 GB), Nintendo GameCube (MiniDVD - 1.5 GB), PlayStation 2, Xbox, Xbox 360, and Wii (DVD - 8.5 GB), and PlayStation 3 (Blu-ray Disc - 50 GB).
Dual-layer Blu-ray Discs can hold about 50 gigabytes (50,000,000,000 bytes), dual-layer HD DVD discs 30 gigabytes (30,000,000,000 bytes) of data.Further Information
Get more info on 'Giga-byte'.
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