Multi-core! What Is It Good For?

What's the killer app for multi-core? There is no single answer.
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At the turn of this century, semiconductor makers were facing a conundrum. Traditionally, they would simply bump up the clock speed to get more performance out of their processors.

After doing this so effectively for two decades, the gimmick was running out of gas. More clock speed meant more heat, and processors have gone from no cooling required to a heat sink that dissipated heat, to heat sinks with large fans that were the size of a Rubik's Cube.

"As AMD and Intel have learned, if you stick with one big core you get one big heating problem," Tony Massimini, chief of technology for Semico Reasearch, told

The solution became multi-core processing. Multi-core is no different from the old days of multiprocessor computers, only instead of two physical chips, there are two cores acting like two CPUs. Windows sees two CPUs, just as it would if there were two physical, single core chips. Two dual-core chips means the system sees four CPUs, and so on.

"Multi-core gives you the ability to divvy up the work for a complex app and be able to then run these cores at lower frequencies," said Massimini. "You are looking at efficient use of power to handle the power dissipation."

AMD released its first dual-core Opteron processors in April 2005 and its first Athlon 64 dual-core processors one month later. Intel went dual core in May 2005 with the Pentium Extreme Edition.

These processors ran in the 2.0GHz to 2.6GHz range, which is slower than the 3.8GHz of the Pentium IV. But the two cores made them execute faster under a workload because of the two cores. They were also cooler, running at around 80 to 90 degrees Fahrenheit on average, as opposed to the 100 to 110 degrees or more of a Pentium IV.

Two cores eventually turned to four for Intel, with its Kentsfield line, released as the Core 2 Extreme line, in November 2006. Clovertown was the first quad-core Xeon processor for servers, also released in November 2006.

AMD will go quad with Phenom and Barcelona on the desktop and server, respectively, later this year.

It's built, but will they come?

So, if Intel (Quote) and AMD (Quote) built all of this technology, will the apps come? Not for a while, it seems. As to what applications parallelization will lend itself to, that's more open to debate.

"There is a class of applications that parallelize very well," Jerry Bautista, director of technology management in the microprocessor research lab at Intel, told "They span from cinematic content creation like Pixar and DreamWorks through home video, gaming and even in financial analytics. These are all a broad class of apps that we typify as taking advantage of model-based computing."

Margaret Lewis, director of commercial solutions for AMD, sees things differently. "The killer app for multi-core is virtualization," she said. "For the desktop it's going to be a little harder for it to take off. In the desktop world, you are one user to a machine. The server is beautiful for multi-core because the server is multiple users, and multiple users means multiple threads."

Virtualization can only happen in the 64-bit world because processors are now free from the restrictions of the 4GB of addressable memory space in a 32-bit processor. A 64-bit chip can, in theory, access 16 exabytes of memory, although hardware vendors are for now sticking to terabytes as the theoretical limit for memory.

"This could only happen with the advent of 64-bits," said Lewis. "The beauty of what's happening is all of these [technologies] are starting to come together to enable virtualization."

Gartner and IDC trends for the last two months reflect this, with fewer machines sold than in the past. But the machines are considerably more "decked out" with much more memory.

One dual- or quad-processor system with 16GB or 32GB of memory is ideal for running dozens of servers in a virtualized environment.

Next page: Programming challenges

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