EXEBYTES OF INFORMATION. Essayist and scientist Philip Morrison ponders the magnitude of recorded information. The ancient library at Alexandria contained about 600,000 scrolls, the equivalent, Morrison estimates, of about 50,000 books. The Library of Congress now holds about 20 million books containing (at roughly a million bytes per book) about 20 terabytes of information. Add to this several petabytes (million billion bytes) in the form of sound recordings. New books and newspapers worldwide account for a bit less than 100 terabytes each year. A century's worth of movies add a petabyte to the accumulation and home pictures (all the snapshots ever taken) another 10 petabytes. According to Morrison, the brightest sources in the information universe are television (100 petabytes per year) and telephony (several thousand petabytes, or exebytes, of audio data annually). Very roughly 100 petabytes of information (mostly TV) are recorded in a form that can (or will) be retrievable. (Scientific American, July 1998.)