Multiple Cores and I

By John Rizzo  |  Posted 2005-02-23 Print this article Print

/O Differences"> The Cell makes up for its simpler Power core by including eight "synergistic processing units" that can work on different tasks in parallel. These multiple cores help the processor run at the high clock rates and with floating point operations that can reach 256 gigaflops (billion floating-point operations per second). However, the Cell isnt IBMs only multicore processor. The Power5 architecture is multicore, as is the forthcoming PowerPC 970MP, which may be Apples choice to receive its PowerPC G6 branding. The chip contains two Power cores that can operate independently and simultaneously. In some reports, the Cell is described as having nine cores, leaving the impression that the Cell is an advanced version over the two-core 970MP. The Cell processors single Power core controls the eight synergistic processing units in a master/slave relationship. In the Cell, the Power-based core is the taskmaster, feeding subtasks to the synergistic processing units.
On the other hand, the two cores in the 970MP are Power-based, each acting separately to handle tasks and operations.
The result of these differences is that the 970MP and Cell excel in different types of tasks. For instance, IBM said the Cells multiple cores will let it run multiple operating systems simultaneously using software virtualization techniques. Each operating system will be run natively, not in emulation. The Cell also will offer outstanding performance for 2-D and 3-D graphics and video—10 times the performance of traditional PC processors, IBM executives said in their Cell briefing. To read more about the Cells virtualization scheme and what that could mean to developers, click here. The PowerPC architecture, currently expressed in 970 family, on the other hand, is designed to run the varied tasks required in a personal computer. Krewell said the first generation of Cell processors appears ill-suited to running a desktop or a mobile PC. "As a general-purpose processor, the Cell might run 10 times slower than what IBM is claiming," he said. Meanwhile, the Cells bus, which is designed by Rambus Inc., is also application-specific, IBM said. "The Cells bus is actually a little more limited because its not designed to be a general-purpose bus," Krewell said. "The Cell [was] optimized for Rambus I/O, which might not be appealing for a mainstream box." The Rambus specs are impressive. For memory, the Cell uses Rambus XDR (extreme data rate), which can provide a total bandwidth of 25.6GB per second. For I/O, the Cell uses FlexIO to pass information outside of the processor. According to Rambus, FlexIO has a maximum bandwidth of 76.8GBps, giving the Cells bus a theoretical bandwidth total of more than 100 GBps bandwidth. No PC processor on the market comes close to that performance. This bandwidth, together with the potential for high gigaflops speed, could make the Cell a graphics powerhouse—which is why Sony is betting the future of the PlayStation platform on it. Assuming the Rambus architecture could be made useful as a general-purpose bus in a PC, the bandwidth probably would saturate todays Mac hardware. The change would require Apple to redesign its bridging controller to interface with the Rambus technology. While this hardware design would not be as difficult as porting the Mac OS X to the new hardware, it would be another hurdle to overcome. Next Page: Future Cells, future Macs.


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