SOI speeds up Motorola chip

Summary:The PowerPC processor has been enhanced by a newer manufacturing process that includes silicon on insulator, which has chiefly been a feature in high-end server chips.

Motorola hopes to prove that it can teach an old chip new tricks.

On Monday, the company launched a new 1GHz PowerPC 7455 chip that is the engine for a new lineup of Apple Computer Power Macs, as well as for new networking equipment.

The new PowerPC, which is part of Motorola's G4 family of chips, boasts higher clock speed and lower power consumption than previous versions of the chip. The enhancements come from a newer manufacturing process that includes silicon on insulator (SOI), which has chiefly been a feature in high-end server chips.

Motorola is the first chipmaker to bring SOI to the desktop. The process places an insulator between a transistor and the silicon bed that a transistor rests upon inside a chip.

The insulator works like a sweater on a cold day. By preventing energy leakage from a transistor into the silicon, it allows a transistor to switch on and off more quickly. Thus, a chip can reach a higher clock speed for a given voltage or use less power to maintain a specific clock speed.

The 1GHz PowerPC runs at 1.6 volts and will consume 15 watts to 17 watts of power, Motorola executives said. Its predecessor, the 533MHz PowerPC 7450, ran at 1.8 volts and consumed 14 watts of power.

"We're always aiming at high performance, but at power levels that make it applicable to our world," said Glenn Beck, director of marketing for Motorola's Computing Platforms division.

The new 733MHz PowerPC 7445, an even lower-power version of the 7455, runs at 1.3 volts and consumes about 10 watts.

The low power consumption of the new chips is important because Motorola sells the majority of its PowerPC chips to networking or other non-PC customers. Often these customers require energy-efficient chips and are willing to give up some clock speed as a tradeoff.

Motorola isn't the only chipmaker looking to bring SOI to the desktop. Advanced Micro Devices has announced plans to offer an Athlon chip sporting IBM's version of SOI technology later this year.

Intel has also discussed a related technology that will be part of a future transistor design it calls the Terahertz transistor.

With AMD and Intel bringing SOI into their chip lines, will Apple lose its newfound SOI advantage over PCs?

Motorola and Apple say no.

Apple asserts that its new high-end Power Macs' dual 1GHz PowerPC chips are up to 72 percent faster than Intel's 2GHz Pentium 4 when running the application Photoshop, for example, because PowerPC chips get more work done with each clock cycle.

"Performance of machines is not really about megahertz. It's about applications performance," Beck said.

The PowerPC's basic architecture, known as RISC, for reduced instruction set computer, is aimed at accomplishing more work per clock cycle, Beck said. Processors from competitors AMD and Intel use the x86 architecture, a design based on the approach known as CISC, or complex instruction set computer.

RISC chips are able to do more work by processing those instructions deemed most important in hardware, while delegating less important instructions to be processed in software. This allows a RISC chip to process more instructions per clock than a competing CISC chip, such as the Pentium 4, because such chips process all instructions in hardware, therefore taking longer to perform some tasks, Beck said.

Motorola, along with Apple and AMD, has been arguing for quite a while that megahertz is not what matters. A potential PC buyer, they assert, should consider overall performance, such as how quickly a PC can perform operations on certain applications.

Meanwhile, aside from a pair of new features that make the chip more networking-friendly, the PowerPC 7455 is similar to its predecessor, the PowerPC 7450.

The PowerPC 7450 chip debuted in January 2001 at up to 733MHz. It has since been deployed widely by Apple in its Power Mac models and its high-end PowerBook portables, and more recently in its new flat-panel iMacs.

Topics: Hardware

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