You know when it's time to get a new car. Your odometer is far into six digits, perhaps the engine is burning lots of oil, or the transmission is growling. Fixing all that might well cost quite a bit more than your ancient vehicle is worth. But what about your microprocessor? Unlike automobiles, microprocessors don't have convenient little gauges that reflect how much wear and tear they've endured. And wear they do-though you'll probably never notice it. The degradation of their transistors over time leads slowly but surely to decreased switching speeds, and it can even result in outright circuit failures.