Computers have made us familiar with the concept of information as a measurable quantity—106 bytes to record a few hundred pages of text or an image from a digital camera, 109 bytes for a 60-minute video streamed from the Internet, and so on. Computers have also made us well aware that the same information can be recorded in many different physical forms: the discs and tapes that we used 25 years ago for our electronic archives have become unreadable on present-day machines.
