When alan greenspan retires in January, after eighteen and a half years as chairman of the Federal Reserve Board, he will have served longer than any previous occupant save William McChesney Martin Jr., who held the job for nearly 19 years. A lot happened during the Greenspan era -- two wars in the Persian Gulf, various currency crises, three stock market meltdowns -- but no topic interested him as much as the revolution in information technology.

Greenspan will ever be associated with the bubble in high-tech stocks -- first for warning, in 1996, that investors might be succumbing to "irrational exuberance," and later, after stock prices had soared and investors truly had succumbed, for presiding over the collapse. Greenspan's critics tend to focus on his enthusiasm for Silicon Valley before the crash; his defenders point out that, after all, the stock market has begun to recover. Both points are somewhat tangential to his real legacy. Greenspan's primary interest was never the precise level of tech-stock prices: it was how the computer was transforming American society.