The terabyte is a multiple of the unit byte
The byte is a unit of digital information in computing and telecommunications that most commonly consists of eight bits. Historically, a byte was the number of bits used to encode a single character of text in a computer and for this reason it is the basic addressable element in many computer...

 for digital information. The prefix
SI prefix
The International System of Units specifies a set of unit prefixes known as SI prefixes or metric prefixes. An SI prefix is a name that precedes a basic unit of measure to indicate a decadic multiple or fraction of the unit. Each prefix has a unique symbol that is prepended to the unit symbol...

 tera means 1012 in the International System of Units
International System of Units
The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...

 (SI), and therefore 1 terabyte is , or 1 trillion (short scale) bytes, or 1000 gigabytes. 1 terabyte in binary prefix
Binary prefix
In computing, a binary prefix is a specifier or mnemonic that is prepended to the units of digital information, the bit and the byte, to indicate multiplication by a power of 2...

es is 0.9095 tebibytes, or 931.32 gibibytes. The unit symbol for the terabyte is TB or TByte, but not Tb (lower case b) which refers to terabit
The terabit is a multiple of the unit bit for digital information or computer storage. The prefix tera is defined in the International System of Units as a multiplier of 1012 , and therefore...



Disk drive sizes are always designated in SI units by manufacturers, which is clearly marked on the packaging. Still, confusion may arise 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 organization
Standards organization
A standards organization, standards body, standards developing organization , or standards setting organization is any organization whose primary activities are developing, coordinating, promulgating, revising, amending, reissuing, interpreting, or otherwise producing technical standards that are...

s such as International Electrotechnical Commission
International Electrotechnical Commission
The International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...

 (IEC), Institute of Electrical and Electronics Engineers
Institute of Electrical and Electronics Engineers
The Institute of Electrical and Electronics Engineers is a non-profit professional association headquartered in New York City that is dedicated to advancing technological innovation and excellence...

 (IEEE) and International Organization for Standardization
International Organization for Standardization
The International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...

 (ISO) recommend to use the alternative term tebibyte
The tebibyte is a standards-based binary multiple of the byte, a unit of digital information storage. The tebibyte unit symbol is TiB....

 to signify the traditional measure of 10244 bytes, leading to the following definitions:
  • In standard SI usage, 1 terabyte (TB) equals = 10004, or 1012 bytes.
  • Using the traditional binary interpretation, a terabyte is = 10244 = 240 bytes = 1 tebibyte (TiB).

The High ISO IEEE number of the terabyte means it can be thought of a physical form of memory, of which the singular byte cannot be.
The capacities of computer storage devices are typically specified using the standard SI meaning of unit prefixes, but many operating systems and applications report in binary-based units. Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...

 10.6 (Snow Leopard) reports SI units.

Illustrative usage examples

Examples of the use of terabyte to describe data sizes in different fields are:
  • Library data – The U.S. Library of Congress
    Library of Congress
    The Library of Congress is the research library of the United States Congress, de facto national library of the United States, and the oldest federal cultural institution in the United States. Located in three buildings in Washington, D.C., it is the largest library in the world by shelf space and...

     Web Capture team claims that "As of April 2011, the Library has collected about 235 terabytes of data" and that it adds about 5 terabytes per month.
  • Online databasesAncestry.com claims approximately 600 TB of genealogical data with the inclusion of US Census data from 1790 to 1930.
  • Computer hardwareHitachi
    Hitachi is a multinational corporation specializing in high-technology.Hitachi may also refer to:*Hitachi, Ibaraki, Japan*Hitachi province, former province of Japan*Prince Hitachi and Princess Hitachi, members of the Japanese imperial family...

     introduced the world's first one terabyte hard disk drive in 2007.
  • Historical Internet traffic – In 1993, total Internet traffic
    Internet traffic
    -Historical Internet Traffic Growth:Because of the distributed nature of the Internet, there is no single point of measurement for total Internet traffic...

     amounted to approximately 100 TB for the year. , Cisco Systems
    Cisco Systems
    Cisco Systems, Inc. is an American multinational corporation headquartered in San Jose, California, United States, that designs and sells consumer electronics, networking, voice, and communications technology and services. Cisco has more than 70,000 employees and annual revenue of US$...

     estimated Internet traffic at 160 TB/s (which, assuming to be statistically constant, comes to 5 zettabyte
    A zettabyte is a unit of information or computer storage equal to one sextillion bytes....

    s for the year).
  • Social networks – As of May 2009, Yahoo! Groups
    Yahoo! Groups
    Yahoo! Groups is one of the world’s largest collections of online discussion boards. The term Groups refers to Internet communication which is a hybrid between an electronic mailing list and a threaded Internet forum, in other words, Group messages can be read and posted by e-mail or on the Group's...

     had "40 terabytes of data to index".
  • Video – Released in 2009, the 3D animated film Monsters vs. Aliens
    Monsters vs. Aliens
    Monsters vs. Aliens is a 2009 American computer-animated 3-D science fiction film produced by DreamWorks Animation and distributed by Paramount Pictures...

    used 100 TB of storage during development.
  • Usenet messages – In October 2000, the Deja News Usenet archive had stored over 500 million Usenet
    Usenet is a worldwide distributed Internet discussion system. It developed from the general purpose UUCP architecture of the same name.Duke University graduate students Tom Truscott and Jim Ellis conceived the idea in 1979 and it was established in 1980...

     messages which used 1.5 TB of storage.
  • EncyclopediaWikipedia
    Wikipedia is a free, web-based, collaborative, multilingual encyclopedia project supported by the non-profit Wikimedia Foundation. Its 20 million articles have been written collaboratively by volunteers around the world. Almost all of its articles can be edited by anyone with access to the site,...

    's January 2010 raw data uses a 5.87 terabyte dump.
  • Climate science – In 2010, Germany's Climate Research Centre (DKRZ) was generating 10,000 TB of data per year, from a supercomputer with a 20 TB memory and 7,000 TB disk space.
  • Audio – One terabyte of audio recorded at CD quality will contain around 2,000 hours of audio. Additionally, one terabyte of compressed audio recorded at 128 kB/s will contain about 17,000 hours of audio.
  • The first 20 years worth of observations by the Hubble Space Telescope
    Hubble Space Telescope
    The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...

     has amassed more than 45 terabytes of data.
  • The IBM
    International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...

     computer Watson, in which Jeopardy!
    Griffin's first conception of the game used a board comprising ten categories with ten clues each, but after finding that this board could not be shown on camera easily, he reduced it to two rounds of thirty clues each, with five clues in each of six categories...

    contestants competed against in February 2011, has 16 terabytes of RAM
    -Animals:*Ram, an uncastrated male sheep*Ram cichlid, a species of freshwater fish endemic to Colombia and Venezuela-Military:*Battering ram*Ramming, a military tactic in which one vehicle runs into another...

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