Is There a Cell Processor in Apples Future?

Reports of a Cell-based Macintosh workstation sent Apple's price upward. But analysts say differences between the Cell and the current PowerPC architectures will make any transition an unlikely prospect for the next few years.

Before and after this months unveiling of the PowerPC-based "Cell" processor, the Mac industry buzzed with predictions that the forthcoming chip would be adopted by Apple Computer as its next-generation computing platform.

While the specs of the new chip are impressive, especially with its integrated support for virtualization and speedy video performance, analysts said differences between the Cell and the current PowerPC architectures will make any transition an unlikely prospect for the next few years.

Besides, use of the Cell chip in a Mac would make sense only if Apple Computer Inc. could get its Mac OS X to run faster than it does on a PowerPC—a task that may prove more difficult than it sounds.

Formally introduced at the International Solid State Circuits conference in San Francisco, the 64-bit Cell processor is a joint project of IBM, Sony Corp. and Toshiba Corp., and will first be used in Sonys PlayStation 3 box.

The group claims that the Cells potential goes beyond gaming, however, extending to everything from cell phones and televisions to high-end Linux workstations. IBM and Sony expect to have prototypes of Cell-based content-creation workstations available in the fourth quarter.


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about the Cells future in gaming boxes and development.

Speculation that Apple will adopt the high-performance Cell was fueled by a Feb. 15 report from Merrill Lynch & Co. Inc. that predicted a Cell-based multimedia workstation from Apple. At the same time, the company raised its Apple stock price objective from $85 to $102 per share, causing Apples stock to jump 4.5 percent in one day.

IBM and Apple declined to comment on Apples possible use of the Cell, but IBM spokesman Glen Brandow emphasized the compatibility between the Cell and the PowerPC.

"User applications for PowerPC will run on the Power Processor Element on Cell," Brandow said. "The Power Architecture remains compliant with applications written for previous, 32-bit, PowerPC processors. The Linux operating system for Cell extends the work for Linux on Power that already exists."

At the rollout event, IBM Fellow Jim Kahle said the Cell supports multiple operating systems, and that a version of Linux is being tested in the lab.

However, some analysts said they think IBMs claims of PowerPC compatibility may be an attempt to persuade Apple to at least consider a porting project to the Cell.

"IBM Micro[electronics] may be trying to entice Apple to get involved," said Kevin Krewell, editor in chief of In-Stat MDRs Microprocessor Report, based in San Jose, Calif. "It would be fairly easy to recompile Mac OS X to run on Cell, but optimizing the OS would be a lot of work."

The optimization difficulties result from the fact the Cell is more like a cousin to PowerPC than a successor, he said. Although both processors are based on IBMs Power architecture, also used in the Power4 and Power5 lines, each processor family uses a different version of the Power architecture.

"Broadband Processor Architecture [BPA] is the formal name for the architecture of the Cell family of processors," Brandow said. "BPA extends the Power architecture with coherent off-load accelerators and real-time management functions."

BPA is designed to process large amounts of information and move it in and out of the processor, and is flexible enough to be reconfigured in future implementations, but is different than the PowerPC architecture.

This is why IBM stresses PowerPC compatibility with the Power Processor Element—the Cells Power-based core. However, Krewell said he thinks the difficulties in optimizing Mac OS X for the Cell arise from differences between the cores of the PowerPC and Cell.

"Even though it runs at over 4GHz, the Cell is has much simpler core than the G5," Krewell said. "Apple might not be happy with the simpler core. The higher clock rate may not buy them much."

For instance, the Cell processor does not perform out-of-order execution, a feature found in most processors designed in the past decade. This type of execution shuffles instructions, executing them without regard to the order in which they were programmed. Cells core also issues fewer instructions.

"The core in the G5 can issue eight instructions at one time," Krewell said. "The Cells core only issues two."

This simpler core design works well in the Cell architecture, but because Mac OS X is built for the more complex PowerPC core, it would require significant modifications in order to see any performance gains over todays Macs, he said.

Next Page: PowerPC G5 versus Cell: multiple cores and I/O differences.