The terabyte is a multiple of the unit byte for digital information. The prefix tera represents the fourth power of 1000, and means 1012 in the International System of Units (SI), and therefore one terabyte is one trillion (short scale) bytes. The unit symbol for the terabyte is TB.
A related unit, the tebibyte (TiB), using a binary prefix, is equal to 10244 bytes. One terabyte is about 0.9095 TiB. Despite the introduction of these standardized binary prefixes, the terabyte is still also commonly used in some computer operating systems, primarily Microsoft Windows, to denote 1099511627776 (10244 or 240) bytes for disk drive capacity.
The prefix tera was defined for the International System of Units in 1960. It is derived from the Greek word τέρας teras, meaning "monster"., but it has also connotation to the Greek word tetra, meaning "four", in analogy to the subsequent prefix names being correlated to magnitude of the decimal exponent.
Usage of terabyte in information technology products includes:
- Database: 1984, Teradata's DBC/1012 is designed to manage a massively parallel processing database up to one terabyte in size.
- Optical disk storage: 1985
- Supercomputer mass storage: ca. 1992 (decimal usage) 
- Supercomputer memory: 2005 (binary usage)
- Hard disk drives: 2007 (decimal usage)
- Tape drives: 2010 (decimal usage)
- Motherboard memory: 2011 (binary usage) 
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 Web Capture team claims that as of March 2014[update] the library had "collected about 525 terabytes of web archive data" and that it was adding about 5 terabytes per month ("one terabyte = 1,024 gigabytes").
- Computer hardware: Hitachi introduced the world's first one terabyte hard disk drive in 2007 (1 terabyte = 1,000 gigabytes).
- SD card: Micron and SanDisk unveiled their microSDXC cards of 1 TB capacity, in February 2019. September 2016 Western Digital (SanDisk) announced that a prototype of the first 1 TB SDXC card will be demonstrated at Photokina.
- How operating systems report drive capacity, Seagate Inc.
- "Windows disk space using TB as a binary value, from Seagate.com". Retrieved 16 April 2018.
- C. Upward, G. Davidson, The History of English Spelling, Wiley-Blackwell (2011)
- Gillin, Paul (February 20, 1984). "Will Teradata revive a market?". Computerworld: 43, 48. ISSN 0010-4841. Retrieved March 13, 2017.
- Pereira, Brian (January 1, 2010). "Marrying Strategic Intelligence with Operational Intelligence". InformationWeek. ISSN 8750-6874. Archived from the original on June 13, 2012. Retrieved March 11, 2017.
- Ishigame, Masaaki (12 April 1985). "Optical Document Filing System With Tera-Byte Capacity". International Society for Optics and Photonics. pp. 106–116. doi:10.1117/12.946440. Retrieved 16 April 2018 – via www.spiedigitallibrary.org.
- Vetter, R. J., Du, D. H., & Klietz, A. E. (1992, March). Network Supercomputing: Experiments with a Cray-2 to CM-2 HiPPI Connection. In Heterogeneous Processing, 1992. Proceedings. Workshop on (pp. 87-92). IEEE.
- Gara, et. al., (2005, March/May). Overview of the Blue Gene/L system architecture. IBM JRD, p.195-212 "32 TB of total memory" (p.203)
- "Hitachi Introduces 1-Terabyte Hard Drive". PCWorld. Retrieved 16 April 2018.
- "Tech Jungle: Tech News and Opinions (by Paul Spain)". www.techjungle.com. Retrieved 16 April 2018.
- "New Intel Server Board to Hold 1 TB of RAM". Retrieved 16 April 2018.
- "Web Archiving FAQs: How large is the Library's archive?". Library of Congress. Archived from the original on 31 July 2014. Retrieved 7 April 2011.
- "Hitachi Introduces 1-Terabyte Hard Drive". PC World. 2007-01-07. Retrieved 2008-09-15.