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COMPUTING SCIENCE

Computing in a Parallel Universe

Multicore chips could bring about the biggest change in computing since the microprocessor

Brian Hayes

Click to Enlarge ImageThe pace of change in computer technology can be breathtaking—and sometimes infuriating. You bring home a new computer, and before you can get it plugged in you're hearing rumors of a faster and cheaper model. In the 30 years since the microprocessor first came on the scene, computer clock speeds have increased by a factor of a thousand (from a few megahertz to a few gigahertz) and memory capacity has grown even more (from kilobytes to gigabytes).

Through all this frenzy of upgrades and speed bumps, one aspect of computer hardware has remained stubbornly resistant to change. Until recently, that new computer you brought home surely had only one CPU, or central processing unit—the computer-within-the-computer where programs are executed and calculations are performed. Over the years there were many experiments with multiprocessors and other exotica in the world of supercomputers, but  the desktops and laptops familiar to most of us continued to rely on a single-CPU architecture whose roots go back to the age of the vacuum tube and the punch card.

Now a major shift is under way. Many of the latest computers are equipped with "dual core" processor chips; they bundle two CPUs on a single slab of silicon. The two processors are meant to share the work of computation, potentially doubling the machine's power. Quad-core chips are also available; Intel has announced an eight-core product, due in 2009; Sun Microsystems has been testing a 16-core chip. A company called Tilera even offers 64 cores. It seems we are on the threshold of another sequence of doublings and redoublings, with the number of cores per chip following the same kind of exponential growth curve that earlier traced the rise in clock speed and memory capacity.

The next computer you bring home, a few years from now, could have hundreds or even thousands of processors. If all goes according to plan, you may notice nothing different about the new machines apart from another boost in performance. Inside, though, coordinating all those separate computational cores is going to require profound changes in the way programs are designed. Up to now, most software has been like music written for a solo performer; with the current generation of chips we're getting a little experience with duets and quartets and other small ensembles; but scoring a work for large orchestra and chorus is a different kind of challenge.




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