BOX 1-1

Units of Size for Data

Bit: The fundamental unit of digital information, equivalent to a 1 or a 0, or to an electronic switch being on or off. Bit is short for binary digit.

Byte: The information stored in eight bits. A byte can be used to store one character of English text.

Kilobyte: The information stored in approximately 1,000 bytes, which is the equivalent of about 15 lines of text.

Megabyte: The information stored in approximately 1,000 kilobytes. A large novel contains about a megabyte of information, and a standard compact disc holds about 680 megabytes of digital information.

Gigabyte: The information stored in approximately 1,000 megabytes. A typical hard drive (as of 2008) holds about 500 gigabytes of information.

Terabyte: The information stored in approximately 1,000 gigabytes. The printed information stored in the Library of Congress equals approximately 10 terabytes.

Petabyte: The information stored in approximately 1,000 terabytes. All U.S. academic research libraries combined contain about 2 petabytes of information.

Exabyte: The information stored in approximately 1,000 petabytes. According to one estimate,a human beings have spoken about 5 exabytes of words over the course of our species’ history.

tity of data being created and stored by businesses, individuals, government, scientific institutions, and individuals is growing rapidly. Figure 1-1 shows one consulting firm’s projection of how information and available storage will grow in the coming years.

This exponential increase in computing power has had profound consequences for many aspects of modern society, including scientific, engineering, and medical research.5 Using digital technologies, researchers can measure, describe, and model phenomena much more comprehensively and in far greater detail than was possible in the past. They can detect and analyze the products


Alexander Szalay and Jim Gray. 2006. “Science in an exponential world.” Nature 440:413–414.

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