The_Trouble_With_Multicore-IEEE_Spectrum - The Trouble With...

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2/15/11 1:53 PM The Trouble With Multicore - IEEE Spectrum Page 1 of 5 Illustration: Harry Campbell COMPUTING / SOFTWARE FEATURE The Trouble With Multicore Chipmakers are busy designing microprocessors that most programmers can't handle By DAVID PATTERSON / JULY 2010 In 1975, future Hall of Famer Roger Staubach had the football but little else in a playoff game against the Minnesota Vikings. Behind by four points at midfield with 24 seconds to go, the Dallas Cowboys quarterback closed his eyes, threw the ball as hard as he could, and said a Hail Mary. (For you soccer fans, this would be like David Beckham taking a shot on goal from midfield late in injury time.) His prayer was answered. Staubach's receiver collided with a Viking defender just as the ball arrived but nevertheless managed to pin the football against his leg, scoring the touchdown that took the Cowboys to the Super Bowl. (Imagine Beckham's long ball beating the goalie.) Ever since that game, a desperate pass with little chance of success has been labeled a Hail Mary. Thirty years later, the semiconductor industry threw the equivalent of a Hail Mary pass when it switched from making microprocessors run faster to putting more of them on a chip—doing so without any clear notion of how such devices would in general be programmed. The hope is that someone will be able to figure out how to do that, but at the moment, the ball is still in the air. Why take such a gamble? In short, because there wasn't much of an alternative. For decades, microprocessor designers used the burgeoning number of transistors that could be squeezed onto each chip to boost computational horsepower. They did this by creating microprocessors that could carry out several operations at once—for example, fetching the next instruction from memory while the current one was being executed. And chipmakers continually upped microprocessor clock rates, something the diminishing size of transistors readily allowed. But around 2003, chipmakers found they could no longer reduce the operating voltage as sharply as they had in the past as they strived to make transistors smaller and faster. That in turn caused the amount of waste heat that had to be dissipated from each square millimeter of silicon to go up. Eventually designers hit what they call the power wall, the limit on the amount of power a microprocessor chip could reasonably dissipate. After all, a laptop that burned your lap would be a tough sell. Designers now accept that although transistors will still get smaller and more numerous on each chip, they aren't going to operate faster than they do today. (Indeed, peak clock speeds are lower now than they were five years ago.) And if you tried to incorporate all those transistors into one giant microprocessor, you might well end up with a device that couldn't compute any faster than the chip it was replacing, which explains the shift to assembling them into multiple
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The_Trouble_With_Multicore-IEEE_Spectrum - The Trouble With...

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