Motorola touts revitalised G4 chip

The PowerPC maker says it's vaulted nagging performance hurdles with the chips in Apple's latest Macs

Motorola says it's moving full speed ahead with the new PowerPC chip that powers Apple Computer's latest Macintosh desktops.

The new chip, called the PowerPC 7450, is the latest offering in Motorola's fourth generation, or G4, of PowerPC processors, and it promises much higher clock speeds and overall performance than earlier revs -- if Motorola can meet delivery expectations. Apple chief executive Steve Jobs announced the new Power Mac models Tuesday at Macworld Expo/San Francisco.

Motorola also posted its fourth-quarter financial results Wednesday, recording big drops in orders for semiconductors and mobile phones.

When it comes to the new chips, "I'm kind of cautious," said Kevin Krewell, senior analyst at Microdesign Resources. "Motorola's ability to deliver in the past has been sort of troublesome."

Motorola's PowerPC troubles erupted in the fall of 1999, when the company was unable to supply 500-MHz PowerPC 7400 chips because of design glitches. Motorola shipped chips at lower promised clock speeds, but the 500-MHz drought lasted until January 2000.

Motorola executives on Wednesday said that the 500-MHz shortage is just a bad memory.

The new chips began production last December, and processors in all four new clock speeds are now shipping, said Brian Wilke, general manager of Motorola's Computing Platform Division. "When you launch a really successful product, one of the challenges is shipping enough of them fast enough," he said. "I would expect that this launch is no different."

"It's not a case where we're having manufacturing glitches of any kind," said Will Swearingen, communications director for the Computing Platforms Division.

Despite bearing a model number close to that of the Power PC 7400, the 7450 chip sports a brand-new architecture. Motorola designed the 7450 chip with higher clock speeds in mind and added a number of tricks to boost overall performance.

The most important design feature is a longer pipeline. By lengthening the pipeline--a structure that prepares instructions to be processed--a chipmaker can boost the clock speed of a processor. The longer pipeline "really lets us turn up the clock and the performance," Wilke said.

Motorola upped the PowerPC 7450 design to seven pipeline stages from the four used in its PowerPC 7400 chip. As a result, the company got a 233-MHz boost in clock speed, initially, and will likely see more megahertz in the future.

The chip saw "a significant increase in clock speed, but more importantly, it's a significant increase in doing real work," Wilke added.

The chip is available in four new clock speeds, ranging from 466 MHz to 733 MHz. Apple is now taking orders on Macintosh desktops with 466-MHz and 533-MHz PowerPC 7450 chips.

While lengthening the pipeline can yield greater clock speed, it can also hurt overall performance, so that the clock speed gains are not in line with actual performance gains. Analysts at Micro Design Resources, which publishes the Microprocessor Report, have taken to calling this the "pipeline tax".

"There's certainly some tax in there, but even at this clock frequency, we're running a significantly shorter pipeline than the other desktop guys," Wilke said.

Indeed, the pipeline of Intel's Pentium III is 10 stages. The Pentium 4 doubled to 20 stages but paid the tax, showing only a small improvement on everyday applications with larger improvements for some multimedia applications. "The more stages, the more you can stall your execution. But you can also get it right," said Mike Feibus, principal analyst with Mercury Research. "You can point to (AMD's) Athlon as a source of the inverse. I don't see anyone complaining about Athlon performance."

Meanwhile, Motorola brought the 256KB of Level 2 cache onboard and increased front-side bus speeds to 133 MHz, two measures aimed at increasing data throughput to the processor. Additionally, the company doubled the amount of AltiVec multimedia instructions its four AltiVec engines can process per clock from one to two. The result should be performance increases when it comes to processing multimedia content such as video.

Citing a desire to not set undue expectations among customers, neither Swearingen nor Wilke would comment on future clock speeds for the PowerPC 7450.

However, the executives did say the PowerPC 7450 would be succeeded by a new line code-named Apollo.

Apollo, announced at last fall's Microprocessor Forum, will pair the Power PC 7450's design with a new manufacturing technology called silicon on insulator (SOI). SOI works to decrease capacitance, or electrical resistance, inside a chip by isolating the chip's transistors from their silicon bed.

The resulting effect is greater performance for the same amount of power consumed or much lower power consumption at a lower clock speed. Apollo chips will hit 1 GHz, the executives said.

With its low power consumption, thanks to SOI, Apollo will also make for a good chip for embedded devices, Motorola's main Power PC market. But at the same time, it will also make an excellent processor for Apple's portable PowerBook line, the executives said.

See Chips Central for daily hardware news, including interactive roadmaps for AMD, Intel and Transmeta.

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