A few weeks ago, I was talking with someone about redundant cells as a route to improved memory yields. I asked whether multiple cores might provide a similar boost for logic chips. My interviewee (who will remain anonymous to avoid embarrassment) didn't seem to think much of the question, suggesting that redundant cores would only make sense for chips with many more cores than are currently available.
So I felt vindicated this week, when AMD both announced a triple-core chip and confirmed that it is based on a quad-core architecture in which "one of the cores is disabled." For instance by a manufacturing defect.
People who've been around a while may remember that Intel pulled a similar trick with the 80486SX microprocessor, which was simply an 80486DX with a defective math coprocessor. And why not? Getting a lower price for a less capable chip is certainly better than adding to the scrap pile.