Making Multicore Fly

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As for PC main memory, today's standard DDR -- double-data-rate SDRAM, also called synchronous dynamic random-access memory -- may not prove fast enough for dual and quad-core systems. DDR2, an emerging successor, should solve that dilemma, Hester says. DDR already works faster than plain SDRAM because it "double pumps" data, to increase memory bandwidth. But DDR2 adds some sophisticated tricks, including memory buffers, to work even faster.

A competing technology, fully-buffered DIMMs (dual in-line memory modules), takes less space on motherboards and could speed up communication between memory and memory controllers. It may help out later; for now, it costs more and draws more power than DDR2.

Power efficiency also ranks as a principal concern for multicore systems. Today, PC makers want to keep power requirements to a minimium, as they create, say, small machines that could reside in a kitchen.

"Some apps won't exploit more than one or two cores," says Hester. "You'd like the processor to realize that," he says, and power down a few cores when they're not in use. This would also help keep the machine quiet -- another priority as computing devices get smaller.

Hardware gurus must also spend time worrying about software. Tomorrow's multicore PC users will need a wide variety of multithreaded programs. Yet the toolkits for building such applications and developers with the skills to do so remain scarce.

"Multithreaded software is hard [to write]," says AMD's Hester. "A lot of programming disciplines don't teach you a lot about writing multithreaded code. That's starting to change." Learning to write efficient algorithms that process information in parallel on two or more cores will be the next major focus for developers of PC software, he says.

Even when developer education and tools catch up, though, not all software will benefit from multicore processing. Some applications will run faster with more cores available, while for others more cores won't make much difference. Image filtering, for example, can be parallelized very efficiently, while video decoding cannot be pushed beyond a certain limit. Multicore also may not make much difference for favorites like Microsoft Word and Excel.

Another software issue: Will vendors have to revise their programs for dual-core processors, then again for processors with more than two cores? Probably not, says Intel's Austin; instead, most vendors will try to code in support for two or more cores from the start.

For years now, the PC industry has dreamed of a revolutionary product that would compel people to buy tens of thousands of new PCs. Will multicore chips that require new software be the ticket? "I don't see additional cores leading to fundamental software breakthroughs," says Rau at IDC. "Multicores will enable us to do what we're doing now -- but better."