One consequence of inexpensive computer memory and storage devices is that much less gets thrown out. People who normally wouldn't characterize themselves as packrats find themselves accumulating megabytes of old email messages, news articles, personal financial data, digital images, digital music in various formats and, increasingly, animations, movies and other multimedia presentations. For many of us, digital memory serves to supplement the neural hardware we were born with for keeping track of things; the computer becomes a sort of neural prosthetic or memory amplifier.

However reassuring it may be to know that every aspect of your digital lifestyle is stored on your computer's hard drive, storing information doesn't do much good if you can't get at what you need when you need it. How do you recall the name of the restaurant your friend from Seattle mentioned in email a couple of years back when she told you about her new job? Or perhaps you're trying to find the recommendation for a compact digital camera that someone sent you in email or you saved from a news article. It's tough remembering where you put things and you'd rather not look through all your files each time you want to recall a piece of information.

In 1999, when NASA launched the first of its Earth Observing System (EOS) satellites, they knew they would have to do something with the terabytes (a terabyte is a billion bytes) of data streaming down from these orbiting observers.