A terabyte is a unit of measurement in computers. Because of irregularities in definition and usage of the kilobyte, the exact number of bytes in a terabyte in common practice could be either of the following values:

1. 1,000,000,000,000 bytes - 10¹². This definition is used in most contexts relating to disk storage, networking, or other hardware.
2. 1,099,511,627,776 bytes - 1024⁴ or 2⁴⁰. This is 1024 times a gigabyte (a binary gigabyte). This is the definition most often used in computer science and computer programming; most software uses this definition.

The symbol for terabyte is TB.

Terabytes in use

A typical video store contains about 8 terabytes of video. The books in the largest library in the world, the U.S. Library of Congress, contain about 20 terabytes of text. The Internet Archive currently has about 1 petabyte of data.

Personal computers containing a terabyte or more of storage space have recently become possible using combinations of high-capacity consumer hard drives. As of 2004, drives exceed 300 gigabytes in size, so storage capacity totalling a terabyte or more can be reached using as few as 3 or 4 hard disks, at a street cost of as little as US$500, down from over US$1000 in 2003. (source: www.pricewatch.com)

A petabyte is either 1000 terabytes or 1024 terabytes, depending on the usage.

Distinction between 1000 and 1024 gigabytes

To clarify the distinction between decimal and binary prefixes, the International Electrotechnical Commission (IEC), a standards body, in 1998 defined new prefixes by combining the International System of Units SI prefix with the word "binary" (see Binary prefix). Thus meaning (2) is called by the IEC a tebibyte (TiB), and meaning (1) is called by the IEC a terabyte. This naming convention has not, as of 2005, been widely adopted.

Origin of prefix

The prefix "tera" properly comes from the Greek "teras" meaning monster, because a trillion is a "monster" number. However, because it happens to be tetra- with one letter out, this model was used for subsequent SI prefixes "peta" and "exa".

See also

• Binary prefix
• integral data type.

External links

• http://www.quinion.com/words/turnsofphrase/tp-kib1.htm
• http://www.nist.gov/public_affairs/techbeat/tb9903.htm
• http://www.wordspy.com/words/yottabyte.asp