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A terabyte is a multiple of the unit byte for digital information. The prefix tera means 1012 in the International System of Units (SI), and therefore 1 terabyte is 1000000000000bytes, or 1 trillion (short scale) bytes, or 1000 gigabytes. 1 terabyte is 0.9095 tebibytes or 931.32 gibibytes using binary prefixes. The unit symbol for the terabyte is TB or Tbyte.


Disk drive sizes are always designated by manufacturers in SI units. However, a possible confusion arises between this measure and 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 unit tebibyte to designate the traditional measure of 10244 bytes, or 1024 gibibytes. Thus, two definitions of the terabyte are in use:

  • In standard SI usage, 1 terabyte (TB) equals 1000000000000bytes = 10004, or 1012 bytes.
  • Using the traditional binary interpretation of SI prefixes, a terabyte is 1099511627776bytes = 10244 = 240 bytes = 1 tebibyte (TiB).

The capacities of computer storage devices are typically specified using the standard SI meaning of unit prefixes, but many operating systems and applications report storage in binary-based units. Mac OS X 10.6 (Snow Leopard) reports SI units.

See also


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