Binary prefix

Binary Prefix

A binary prefix is a unit prefix for multiples of units in data processing, data transmission, and digital information, notably the bit and the byte, to indicate multiplication by a power of 2.

Definition

The computer industry has historically used the units kilobyte, megabyte, and gigabyte, and the corresponding symbols KB, MB, and GB, in at least two slightly different measurement systems. In citations of main memory (RAM) capacity, gigabyte customarily means 1073741824 bytes. As this is a power of 1024, and 1024 is a power of two (2^10), this usage is referred to as a binary measurement.

History

In 1998 the International Electrotechnical Commission (IEC) published Amendment 2 to international standard IEC 60027-2, which specified the binary prefixes kibi (Ki), mebi (Mi), gibi (Gi), tebi (Ti), pebi (Pi), and exbi (Ei). However, this standard has not been widely adopted in the computing and networking industries.

Usage

The binary prefix kibi is derived from the prefix kilo and binary, meaning 2^10. The rest of the prefixes were similarly derived. These prefixes are now part of the International System of Quantities. The IEC further specified that the kilobyte should be used only for 10^3 bytes, the megabyte for 10^6, and so on.

Controversy

The use of the same unit prefixes with two different meanings has caused confusion. Starting around 2005, many hard disk manufacturers use decimal prefixes, which are defined by international standards, meaning that a 1 KB file does not occupy 1024 bytes but 1000 bytes.

See also

• Byte
• Bit
• Data rate units
• Orders of magnitude (data)