Close but No Cigar

1. Speedwalking

2. America Online, CompuServe, and Prodigy

3. Veggie burgers

4. Using a StairMaster

5. Winning the Wild Card pennant

6. Driving 55 mph

7. Living in suburbia

8. New Year's resolutions

9. Lists as poetry

10. Lists as a simple way to give structure to humor

11. Cigarettes

3.1 Correcting Errors

The theory of computers rests on an immutable foundation: a bit is either on ("1") or off ("0"). Underneath this foundation, however, is the normal, slightly random, slightly chaotic world in which humans spend their time. Just as the sun is sometimes a bit brighter than usual and sometimes it rains for a week straight, the physics that govern computer hardware is a bit random. Sometimes that spot on the hard disk that is responsible for remembering something doesn't behave exactly perfectly. Sometimes an alpha particle from outer space screams through a chip and changes the answer.

Computer designers manage to corral all this randomness through a mixture of precision and good mathematics. Clean machines eliminate the dirt that screws up things, and the mathematics of error-correcting codes is responsible for fixing up the rest of the problems that slip through. This mathematics is really one of the ideas that is most responsible for the digital explosion. The math makes it possible to build a digital circuit with a bit of sloppiness that can never be present in an analog world. Designers know that the sloppiness can be fixed by a bit of clever mathematics.

Error-correcting codes can be used effectively to hide information...