The power and speed of modern digital computers is truly astounding. No human can ever hope to compute a million operations a second. However, there are some tasks for which even the most powerful computers cannot compete with the human brain, perhaps not even with the intelligence of an earthworm. Imagine the power of the machine which has the abilities of both computers and humans. It would be the most remarkable thing ever. And all humans can live happily ever after (or will they?). Before discussing the specifics of artificial neural nets though, let us examine what makes real neural nets - brains - function the way they do. Perhaps the single most important concept in neural net research is the idea of connection strength.