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Prefixes for bit and byte multiples
Value SI
1000 k kilo
10002 M mega
10003 G giga
10004 T tera
10005 P peta
10006 E exa
10007 Z zetta
10008 Y yotta
1024 Ki kibi K kilo
10242 Mi mebi M mega
10243 Gi gibi G giga
10244 Ti tebi
10245 Pi pebi
10246 Ei exbi
10247 Zi zebi
10248 Yi yobi

A terabyte (or Tbyte) is a SI-multiple (see prefix tera) of the unit byte for digital information storage and is equal to 1012 (1 trillion short scale) 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 would be 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.

Examples of terabyte usage

Examples of the use of "terabyte" to describe data sizes in different fields are:

  • Library data - The U.S. Library of Congress Web Capture team has claimed that "As of May 2009, the Library has collected almost 100 terabytes of data".[1]
  • Online data bases - claims approximately 600 TB of genealogical data with the inclusion of US Census data from 1790 to 1930.[2]
  • Computer hardware - Hitachi introduced the world's first one terabyte hard disk drive in 2007.[3]
  • Internet traffic - In 1993, total Internet traffic amounted to approx. 100 TB for the year.[4] As of June 2008, Cisco Systems estimated Internet traffic at 160 TB/s (which assuming to be statistically constant comes to 5 zettabytes for the year).[5]
  • Social networks - As of May 2009, Yahoo! Groups had "40 terabytes of data to index" [6]
  • Video - Released in 2009, the 3D animated film Monsters vs. Aliens used 100 TB of storage during development.[7]
  • Usenet messages - In October of 2000, the Deja News Usenet archive had stored over 500 million Usenet messages which used 1.5 TB of storage[8]

See also


  1. ^ "How large is the Library's archive?". 2007-05-26. 
  2. ^ " Adds U.S. Census Records". 2006-06-22. 
  3. ^ "Hitachi Introduces 1-Terabyte Hard Drive". PC World. 2007-01-07. Retrieved 2008-09-15. 
  4. ^
  5. ^ White, Bobby (2008-06-16). "Cisco Projects Growth To Swell for Online Video". The Wall Street Journal. 
  6. ^ "Yahoo! Groups Blog". 2009-05-09. 
  7. ^ IRENE THAM (2009-04-08). "Taking a monster hit; Massive computer power was needed to create the 3-D movie Monsters Vs Aliens.". The Straits Times. "The 3-D movie used up close to 100 terabytes of disk space and more than 40 million hours of rendering." 
  8. ^ "Usenet Sale: Sounds to Silence?". 2000-10-25. Retrieved 2009-10-13. "It's loaded with 500 million postings ... [and has] ballooned to over 1.5 terabytes" 

Simple English

A terabyte (TB) is a unit of measurement in computers and similar electronic devices. Terabytes hold 1000 gigabytes (GB) or a trillion (1,000,000,000,000) bytes, and 1000 terabytes make one petabyte. Some people say that the exact number of bytes is 1,099,511,627,776.[needs proof] The correct term used for this exact figure is tebibyte.

Large organisations use terabytes of storage to hold massive amounts of data. People at home probably do not use terabytes, they would use gigabytes, megabytes and occasionally kilobytes. However, in the future terabytes of storage will probably be more common in home usage. In fact, according to this page on the Apple website, 2008 Apple iMac computers can be ordered with 1 TB hard drives. An external hard drive can be several terabytes. Usually, one terabyte of space costs between 100 and 150$.[1]


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