Prescott not expected to duplicate IBM power savings

Internal IBM Corp. documents posted on its Web site indicate that the company engineered a substantial reduction in the power consumption of one of its forthcoming 90 nanometer processors, while Intel Corp.'s 90 nanometer Prescott chip is expected to show little to no change in power consumption.

Prescott is expected to make its debut at the beginning of February, and it is also expected to be the first processor developed on a 90-nanometer process technology to hit the open market. IBM's PowerPC 970FX chip will be released later in the year.

The IBM documents, first reported by The Register Thursday, show that the PowerPC 970FX typically consumes 24.5 watts of power when running at 2.0GHz. This compares to the 51 watts typically consumed by the current PowerPC 970 chip when running at 1.8GHz.

An IBM spokesman declined to comment on the specifications, but said more details about the chip would be presented Feb. 16 at the International Solid State Circuits Conference in San Francisco. The documents are available on IBM's Web site at$file/PPC_QRG_1-22-04.pdf

Apple Computer Inc. uses the 970 in its PowerMac G5, and is expected to use the 970FX in a new PowerMac as well as a new XServe rack server, both of which will probably be available in February right about the same time IBM presents details about the 970FX, said Peter Glaskowsky, editor in chief of the Microprocessor Report in San Jose, California.

After talking to Apple executives about the new XServe following its introduction at MacWorld earlier this month, Glaskowsky discovered that the 970FX will consume about 55 watts at maximum power when clocked at 2.0GHz, he said.

Intel has already disclosed a few details about Prescott's architecture. The chip will come with 1M bytes of Level 2 cache, double the cache of current Pentium 4 processors. It also contains 13 new instructions that help improve the performance of multimedia programs and applications that require floating point performance.

Analysts expect the chip to debut at 3.4GHz with other versions at slower clock speeds, and expect the 3.4GHz chip to consume about 90 watts at maximum power. The maximum power consumption of a processor usually comes into play only when the chip is tackling complex tasks, but motherboard designers must keep that number in mind when designing their products.

The current leader in Intel's Pentium 4 stable, the 3.2GHz chip with 512K bytes of cache, needs 82 watts of power at maximum consumption. The Pentium 4 Extreme Edition consumes more power, and is said to outperform the regular Pentium 4, but features 2M bytes of Level 2 cache.

Usually, the jump to a new process technology allows chip designers to reduce the power consumed by their chips when comparing two chips built on different process technologies that use the same architecture and run at the same clock speed. But as chip makers reduce the average feature sizes of their chips to 90 nanometers, the structures on the chips become so small that electrons can sometimes leak out as heat.

This heat can be disruptive to system performance, and can require more expensive cooling equipment to prevent the system from shutting down.

If the expectations of 90 watts are correct, Intel will not have realized any power savings from moving to a new process generation. The new instructions and increased cache appear to have eaten up any power savings, but current leakage could also have played a role, analysts have said.

Some analysts have attributed IBM's power savings to its use of silicon-on-insulator (SOI) technology. SOI is a process by which IBM builds transistors atop a thin layer of silicon that is placed over an insulating material such as silicon oxide in order to insulate the circuit against power leakage.

Intel has thus far disdained SOI for reasons of cost, opting instead to use techniques such as strained silicon in its 90 nanometer process generation. Strained silicon is formed by adding a layer of silicon germanium atop a silicon wafer. The atoms in the two substances seek to align with each other, stretching the silicon and freeing more space for electrons to travel.

IBM and Intel rival Advanced Micro Devices Inc. both use SOI in manufacturing some of their current processors as well as their 90 nanometer versions.

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