Fast Forward: Multicore vs. Manycore

Nathan Edwards

In the last few years, PC processors have exploded from single-core designs to dual-core and now quad-core chips. The first eight-core PC processor will probably appear by the end of this decade. Beyond that, 12- and 16-core chips are possible. What then?

Some CPU architects believe the current road is a dead end, much like the pursuit of superfast clock speeds with single-core processors. Although the x86 cores that AMD and Intel use in their multicore chips are more efficient than previous cores were, today’s cores are still too large and power hungry to sustain the momentum of multicore progress. Some engineers argue that multicore chips must give way to “manycore” chips.

What’s a manycore chip? There’s no hard definition. Basically, it’s a microprocessor with tens, hundreds, or even thousands of processor cores. It’s like multicore on fertility pills.
Intel recently hinted at this future by showing an 80-core chip, code-named Polaris. It caused a stampede of breathless coverage in the mainstream press and on technology websites. However, Polaris is strictly a prototype, not a product. Its 80 cores are relatively simple FPUs, not x86-compatible cores. Polaris is based on an experimental VLIW architecture optimized for floating-point math.

In reality, Intel is playing catch-up in this race. Other companies have already produced manycore processors with hundreds or thousands of cores. I’m talking about finished designs in actual production, not lab experiments. Manycore processors are running today in real-world applications, such as base stations for wireless networks.
Nevertheless, Polaris is an important star to steer by. The reason: Intel has another project to develop a low-power x86 core for ultramobile PCs and embedded systems. This core will probably consume less than one watt. Intel could use it to build manycore processors for desktops, notebooks, and servers, too. Such processors could have 100 or more cores without a meltdown.

Of course, manycore processors don’t solve the problem of writing parallel-processing software that usefully exploits so many cores. Manycore chips might also reveal software bugs that bite only when running numerous threads (see last month’s column). But for CPU architects, there’s little choice. If multicore processors reach a dead end, as high-frequency single-core processors did, then manycore processors might be the only alternative.

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