IBM: PowerPC G5 to Go Mobile

 
 
By Mark Hachman  |  Posted 2004-06-25
 
 
 

IBM: PowerPC G5 to Go Mobile


The 64-bit PowerPC G5 processor will undoubtedly be a fixture of Apple CEO Steve Jobs keynote next weeks Worldwide Developers Conference. After all, its the basis of the companys workstation and server lines. But Mac professionals, and even Linux programmers, will be waiting for word of a mobile version.

According to officials of IBM Corp., the technology for a notebook version of the PowerPC G5, a k a the PowerPC 970 series of processors, may be at hand.

IBMs PowerPC 970 family of microprocessors has quietly become a rarity in the computing world: a one-size-fits-all architecture used for notebooks, desktops and even low-end servers. The chip is based on the companys longstanding POWER architecture, a dual-core processor used in some of IBMs server lines.

Now, IBM is being asked to migrate those chips into the crucial notebook market while simultaneously designing an architecture that can be competitive in low-end servers.

Norman Rohrer, chief designer of the PowerPC 970FX chip used in Apples Power Mac G5 desktops and Xserve servers, said the same chip that IBM uses for its desktop machines can also be used comfortably within future PowerBook notebooks through a power-management technique called "PowerTune." Industry insiders said a PPC 970FX-based notebook is not expected to ship before the end of the year, however.

At the same time, a small-form-factor iMac would require a similar thermally managed processor. Reports recently circulated that Apple will introduce a G5-based iMac at WWDC in San Francisco.

In addition, Merrill Lynch & Co. Inc. vice president and analyst Steven Milunovich on Wednesday published a note to clients predicting that a redesigned iMac would debut next week at the WWDC.

One retailer interviewed by eWEEK.com said supplies of the G4-based iMac have slowed, consistent with Apples strategy just before a refresh of the product line. But the retailer could not confirm that a G5 iMac would be announced next week. However, other industry watchers said that same trend would occur for any refresh of the line, whether with the G5 or a faster PowerPC G4 processor.

An Apple representative declined to comment.

For insights on the Mac in the enterprise, check out eWEEK.com Executive Editor Matthew Rothenbergs Weblog.

IBMs design goal with PowerTune is to balance performance and power consumption. In addition, because the "leakage current"–the amount of power that trickles away and is wasted–is significantly higher at finer process technologies, such as used for the 970FX, IBM developed PowerTune.

The design approach somewhat differs from rival Intel Corp., which places as much emphasis on manufacturing as it does on design, if not more. While Intel has aggressively pushed new process technologies into the market, IBM has concentrated upon process improvements, such as silicon-on-insulator and doped silicon. Using materials with a low threshold voltage can improve the clock speed of a chip, but also increases the power lost to leakage current, IBMs Rohrer said.

"If you optimize the process you can not leak as much in the portable space," Rohrer said.

The 970FXs design is more efficient than the older PowerPC 750FX, part of the G4 family of processors. It contained two PLL (phase-locked-loops) circuits, designed to shift the processor quickly into a low-power state in just three clock cycles.

Instead, the G5 PowerTune design is based on a single PLL that can shift the processor into several low-power states in a single clock cycle.

The PLL will be locked to a single frequency, simplifying the synchronization of circuitry, Rohrer said. Instead, a multiplexer will divide the bus speed, thus slowing the chip. This scheme is the opposite of desktop processors, where the processor often runs at some greater multiple of a given bus speed. The frequency switch will not be limited to the processor core but also manage the processor bus, the I/O bridge and the memory controller.

For example, PowerTune-savvy chip can be asked to drop down to a half or a quarter the rated frequency, or even down into a "deep nap" state where the chip can run at 1/64 of the rated frequency, Rohrer said.

Within each frequency iteration, the processor also can be instructed to run in idle or nap modes, which will reduce the operating voltage of the chip. The combination of voltage and frequency scaling, Rohrer said, will be PowerTunes advantage, and is a much more flexible power-management scheme than its x86-compatible competitors.

Moreover, power modes can be entered and left relatively quickly, "on the order of several microseconds," Rohrer said. "Anytime you pause on the keyboard, after the time the system has to finish the last instruction, the system can enter deep nap."

Next Page: Bridging Notebooks and Servers with One Architecture.

Bridging Notebooks and Servers


with One Architecture">

But the kicker for IBM and its customers is that the PowerPC 970FX is a one-size-fits-all architecture that accommodates servers as well as notebooks.

"The portable-space specs that are out there talk about 15 to 30 watts for maximum power. We want to be inside that envelope," Rohrer said. "The low-frequency operating conditions in the idle state—nap—are in the 1- to 2-watt range."

That will mean that any G5 notebooks will likely be clocked somewhat lower than the current G5 desktops.

In one hypothetical example of a low-power state, Rohrer said a PowerPC 970FX in the 1/64 "deep nap" state could run at 30MHz, which would equate to about 1.9GHz in full-speed mode. Apples shipping dual-processor G5 desktops range in speed from 1.8GHz to 2.5GHz.

"Thats the whole intention of this, to make it usable in low-end servers ... down into portables," Rohrer said. "To do that, you cant start with high voltage and high frequency; you cant hit 50 watts. Youve got to start with a lower voltage and lower frequency and [then] adjust the voltage and drop the frequency."

This multi-use approach is much different from that of IBMs rivals. "IBM cant afford to spend the amount of money developing multiple architectures that Intel [Corp.] can," said Nathan Brookwood, principal analyst at Insight64 in Saratoga, Calif.

"Because of its market share, because of its growing share in the mobile market, Intel can afford to send a few engineers off to optimize a mobile processor," Brookwood said. "Youre not likely to see that kind of effort from IBM.

"The mobile PowerPC market is relatively small, even though there are an increasing number of PowerBooks," he said. "If you look at Apples market share in the PC industry, and then [compare] their desktops versus their notebooks, its hard to justify the same kind of R&D Intel put into Centrino."

The issue is actually a critical one for Apple. For all the concerns about IBMs manufacturing capabilities, architecting a low-power processor for notebooks may actually be more important.

Although the G5 processor was first introduced within a desktop Macintosh, currently, the G5 minitowers actually represent the minority of unit shipments for Apple, based in Cupertino, Calif. In April, Apple reported second-quarter sales of 711,000 Macintosh units, of which 42 percent or about 298,600 were notebooks, Apple executives said.

Sales of Apples entry-level iMac line totaled 256,000 units, or about 37 percent of the total. The remainder consisted of Apples desktops, about 21 percent of all Macintosh units sold.

Penetrating all of the available markets is critical, analysts said. In the past, Advanced Micro Devices Inc. sales have been hurt, some analysts said, because its Athlon64 architecture didnt scale down easily into the "thin and light" notebooks that dominate the notebook sector.

However, AMD began selling mobile versions of its Athlon XP in May, and it is developing a stripped-down Sempron chip to address the low-end desktop and mobile markets.

"IBM designed the PowerPC 970 as a desktop part: high-frequency, high-performance and also for servers," said Kevin Krewell, an analyst at In-Stat/MDR in San Jose, Calif.

Next Page: Should IBM Break out Mobile and Server Designs?

Should IBM Break Out


Mobile and Server Designs?">

When asked if IBM needs to develop a Pentium M-style redesign, Krewell responded, "I would hope they would. I think thats the way you need to go to get something like the Athlon64 into the notebook. Big, transportable things with a lot of power and a lot of fans arent Apples business model. Apple has to be more stylish."

IBMs designers disagree. Rohrer said with PowerTune, the G5 will likely be down-clocked to enable it to enter the 15- to 30-watt range needed to produce a G5 notebook.

A dual-core version of the processor could also boost performance at slower speeds. Rohrer declined to confirm whether a dual-core PowerPC is on the companys roadmap, although he did say that a dual-core chip would remove some of the pressure to constantly push clock speeds higher.

AMD and Intel say they will release dual-core chips in 2005. Click here to read more.

IBMs current 2.5GHz PowerPC 970FX chip runs more efficiently, consuming about 50 watts under a typical load, which will vary according to how computationally intensive the application is. The previous PowerPC 970, manufactured on a coarser, 130nm process, required 66 watts under a typical load. But IBM to date has not disclosed the maximum thermal power the chips can consume, muddying the question of the chips thermal envelope.

Its unlikely, analysts added, that Apple will take on the Intel Centrino and Transmeta Corp.s Crusoe in the ultraportable notebook space, at least in the near term.

Click here to read about Linux drivers for Centrino, which Intel said will be available this year.

While keeping one eye on desktops and mobile concerns, IBMs chip group also must keep the other on server applications, such as Apples Xserve server and its own dual-processor, PowerPC 970FX-based JS20 blades. Some 2,282 of the blade servers were recently combined to form a supercluster for the Spanish Center for Supercomputing.

Apples G5 desktops, the IBM blades and the Xserve use two discrete processors to handle computational tasks. Intel and AMD, on the other hand, have announced plans to combine two processor cores on the same chip, a strategy employed by IBMs POWER5 core for multiprocessor servers. Since the G5 was based on the Power4 architecture, a future, multicore PowerPC is a natural assumption.

Rohrer declined to comment on IBMs plans for future products, including the PowerPC 975, a rumored successor to the PowerPC 970 family.

Instead, Rohrer postulated a dual-core conundrum: On one hand, adding two cores reduces the workload on the overall computing unit, so a chip doesnt have to be clocked as fast. Clocking down the individual cores is also necessary, Rohrer said, for designing a multicore chip inside the same thermal constraints as a unicore processor.

On the other hand, buyers still will compare chips using the rated frequency. "We all do specmanship," he said. "Its hard to get away from frequency. Its the easiest apples-to-apples comparison you can make."

To read about Intels plan to play down clock speeds in its new naming plan, click here.

Analyst Brookwood said a dual-core PowerPC seems like a logical step. Apples Xserve generates a reasonable amount of volume, he said, and a more power-efficient, multitasking environment is a selling point for the PowerPC. "PowerPCs are typically going to workstation-class products," he said. "A dual-core processor makes a lot of sense."

Check out eWEEK.coms Macintosh Center at http://macintosh.eweek.com for the latest news, reviews and analysis about Apple in the enterprise.

Be sure to add our eWEEK.com Macintosh news feed to your RSS newsreader or My Yahoo page

Editors Note: This story was updated on June 26 at 11:45 PM PDT to add a quote from IBMs Rohrer on manufacturing processes. The quote was accidentally omitted through an editing error.

Rocket Fuel