Since the first disk drive, the
IBM 350, disk drive manufacturers expressed
hard drive capacities using decimal prefixes. With the advent of gigabyte-range drive capacities, manufacturers labelled many consumer
hard drive,
solid-state drive and
USB flash drive capacities in certain size classes expressed in decimal gigabytes, such as "500 GB". The exact capacity of a given drive model is usually slightly larger than the class designation. Practically all manufacturers of hard disk drives and flash-memory disk devices
iOS,
Android,
Ubuntu, and
Debian express hard drive capacity or file size using decimal multipliers, while others such as
Microsoft Windows (including
Windows Phone) report file size using binary multipliers. This discrepancy causes confusion, as a disk with an advertised capacity of, for example, (meaning , equal to 372 GiB) might be reported by the operating system as "". For
RAM, the
JEDEC memory standards use
IEEE 100 nomenclature which quote the gigabyte as (230 bytes). 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 more pronounced.
US lawsuits A lawsuit decided in 2019 that arose from alleged breach of contract and other claims over the binary and decimal definitions used for "gigabyte" has ended in favour of the manufacturers, with courts holding that the legal definition of gigabyte or GB is 1 GB = 1,000,000,000 (109) bytes (the decimal definition). Specifically, the courts held that "the U.S. Congress has deemed the decimal definition of gigabyte to be the 'preferred' one for the purposes of 'U.S. trade and commerce'. ... The California Legislature has likewise adopted the decimal system for all 'transactions in this state'." Western Digital settled the challenge and added explicit disclaimers to products that the usable capacity may differ from the advertised capacity.
Other contexts Because of their 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 (10243 B) is conveniently expressed as 1
GiB rather than as 1.074 GB. The former specification is, however, often 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 capacities and rates, like
storage hardware size,
data transfer rates,
clock speeds,
operations per second, etc. are usually presented in decimal units. For example, the manufacturer of a "300 GB" hard drive is claiming a capacity of , not 300 × 10243 (which would be ) bytes. ==Examples of gigabyte-sized storage==