A terabyte is a SI-multiple (see prefix tera) of the unit byte for digital information storage and is equal to 1012 (1000000000000) bytes or 1000 gigabytes. The unit symbol for the terabyte is TB.
The designation terabyte is rarely used to refer to the tebibyte, its binary prefix analogue, because only recent (since 2007) disk drives have this capacity. Disk drive sizes are always designated in SI units by manufacturers. However, a possible confusion arises from this definition with the long-standing tradition in some fields of information technology and the computer industry of using binary prefix interpretations for memory sizes. Standards organizations such as International Electrotechnical Commission (IEC), Institute of Electrical and Electronics Engineers (IEEE) and International Organization for Standardization (ISO) recommend to use the alternative term tebibyte to signify the traditional measure of 10244 bytes, or 1024 gibibytes, leading to the following definitions:
* In standard SI usage, 1 terabyte (TB) equals 1000000000000bytes = 10004 or 1012 bytes.
* Using the traditional binary interpretation, a terabyte is 1099511627776bytes = 10244 = 240 bytes = 1 tebibyte (TiB).
The capacities of computer storage devices are typically specified using their the standard SI meaning of unit prefixes, but many operating systems and applications report in binary-based units. Mac OS X 10.6 (Snow Leopard) reports decimal units.