The gibibyte is a multiple of the unit byte for digital information. The binary prefix gibi means 230, therefore one gibibyte is equal to 1073741824bytes = 1024 mebibytes. The unit symbol for the gibibyte is GiB. It is one of the units with binary prefixes defined by the International Electrotechnical Commission (IEC).
The gibibyte is very closely related to the gigabyte (GB). The GB is defined by the IEC as 109 bytes = 1000000000bytes, 1GiB ≈ 1.074GB. 1024 gibibytes are equal to one tebibyte. In the context of computer memory, Gigabyte and GB are customarily used to mean 10243 (230) bytes, although not in the context of data transmission and not necessarily in the context of hard drive size. The word gibibyte was coined in 1998.
Hard drive and SSD manufacturers use "GB" to mean 1000000000 bytes. So, the capacity of a "128 GB" SSD will be 128000000000 bytes. Expressed in GiB this would be about 119.2 GiB (128000000000 divided by 1073741824). Many operating systems, including Microsoft Windows, will display such a drive's capacity as "119 GB", using the SI prefix "G" but in the "binary" sense. No space is "lost" or "missing". The size is simply being expressed in a different unit, even though the "G" prefix is used in both cases.
The use of "GB" or "gigabyte" to refer to 1000000000 bytes in some contexts and to 1073741824 bytes in others, sometimes in reference to the same device, has caused some confusion among consumers. In a few cases this has led to legal challenges against the makers of storage devices. (For more details, see Binary prefix#Legal disputes.)
Apple's MacOS X v10.6 and later changed their displays of file and drive sizes to use SI prefixes in their SI-defined, or decimal, sense, so the same "128 GB" drive would appear as "128 GB" on such systems. Confusion is still possible as it is not clear from such a display that the SI meaning of the prefix is being used, particularly as MacOS X continues to use the SI prefixes to mean powers of 1024 in their displays of RAM capacity.
The IEC created "gibi" and other binary prefixes (kibi, mebi, tebi, etc.) in an attempt to reduce such confusion, but these prefixes have yet to see widespread adoption . They are, however, increasingly used in technical literature and open-source software, and are a component of the International System of Quantities.