August 17, 2003 9:00 PM PDT

Sun's Gemini mixes old with new

Sun Microsystems plans next year to come out with a new line of microprocessors for dense servers that will wed cutting-edge design concepts with a chip from the 1990s.

Gemini, the first chip in a new line of "h series" microprocessors to be launched in 2004, will contain two processor cores, the brains inside a chip, into the same piece of silicon, said Harlan McGhan, strategic marketing manager of UltraSparc at Sun.

Although inserting two cores into one piece of silicon is a relatively recent phenomenon, the processor cores inside Gemini don't come from Sun's premier line of microprocessors, the UltraSparc III. The company is recycling the core out of the UltraSparc II, a chip the company hasn't advanced since 1999.

Mixing the old and new, however, has practical advantages. For one thing, it will allow Sun to get to market relatively quickly; the chip will be launched after only 24 months of work, McGhan said.

Using the older core also allows Sun to keep power consumption relatively low, a necessity for blade servers and rack-mounted servers. Low power consumption leads to less ambient heat, which means more servers can be packed into a single computer room--a plus for many companies.

"What is Google's biggest concern?" McGhan gave as an example. "They'd like to pack more computers into a room. The UltraSparc II core is extremely efficient."

Escalating consumption of energy, combined with the difficulty and expense of following Moore's Law, has sparked an era of creativity in chip design, prompting engineers to look at novel chip designs and new materials to advance performance.

IBM, for instance, won plaudits from analysts with the Power 4, the first server chip to feature two cores. Intel, meanwhile, introduced hyperthreading, which allows a chip to run two applications, or two threads of the same application, at the same time. Intel also is on the verge of introducing products with strained silicon, which reduces energy consumption and lets chips run faster.

Sun's strategy for its processors and servers is called "throughput computing." The overarching concept explores how to maximize the number of simultaneous calculations while minimizing the energy involved.

"The question is, 'How are you going to spend those transistors?'" McGhan said.

Gemini can be called a 2-1-4 chip, he said, meaning that the chip has two cores, and each core can handle one application thread and four instructions (or tasks) per thread at once. In all, that means eight simultaneous functions.

The successor chip, called Niagara will come with eight cores, and each core will handle four threads with one instruction per thread at once, for a total of 32 instructions.

Performance boost
Why is there a shift toward cores and threads and away from performing multiple instructions at once?

Adding an additional core boosts performance by 80 percent to 90 percent, McGhan said, because it's like getting an extra chip for free. Sun came out with a dual-core multimedia chip, called MAJC, earlier but it never made much of a dent commercially.

Multithreading achieves a similar effect: More applications can be processed at once, so the computer thinks it is dealing with two different chips. The performance boost is far less--around 10 percent to 30 percent, according to various industry estimates--but it's still a substantial gain.

Performing multiple instructions per thread simultaneously was a design technique that was hot for years, but the performance gains have bottomed out, McGhan said.

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"Changing thread level performance is not paying off," he said. If such a shift away from executing multiple instructions in a single thread were theorized two to three years ago, McGhan would have "suggested a place where you could get your head examined."

Gemini will debut at speeds in the 900MHz to 1.2GHz range, according to Sun. Among other features, it contains a 1MB cache, although each core can only access 512KB of cache. Gemini will consume between 14 watts and 32 watts, depending on the speed it is running.

The chip will be made on the 130-nanometer process, which means that the average size of features inside the chip will measure 130 nanometers. (A nanometer is a billionth of a meter.) The last UltraSparc II that Sun released was made on the 250-nanometer process. Sun essentially jumped two manufacturing generations with this chip, skipping the 180-nanometer process entirely.

The smaller dimensions of the chip will allow Sun to use the same package and other technology associated with its UltraSparc IIIi, a version of the UltraSparc III for lower-end servers. As a result, Sun won't have to do a complete redesign of the UltraSparc IIIi server to adopt Gemini.

Servers containing the chip will come out toward the middle of 2004, while computers running Niagara will debut in the second half of 2005 or the first part of 2006.

The company will present details on Gemini next week at Hot Chips, an annual semiconductor design conference at Stanford University.

Among other expected conference highlights, IBM will unveil details about the Power5 processor.

Also on full display at the conference will be the international supercomputer rivalry. On Monday, scientists from Los Alamos National Laboratory and Cray will provide details on Red Storm, a supercomputer designed around the Opteron processor from Advanced Micro Devices.

Immediately afterward, Tadashi Watanabe, vice president of high-performance computing at NEC, will give a talk on Earth Simulator, the world's most powerful computer. Earth Simulator has sent shivers through Washington and has prompted policymakers to review the federal government's supercomputing policies.

 

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