The machine that could

Indeed, IBM did target the high-end computing market: in 2008 it built the world’s most powerful supercomputer to model the decay of the US nuclear arsenal for the Los Alamos National Laboratory. Roadrunner, a $100m system with 12,960 Cell chips (now 60nm with added memory) and 6,480 AMD Opteron dual-core processors, became the world’s first machine to sustain 1.0 petaflops using the Linpack benchmark, roughly double the performance of the next best system.

“In retrospect, if you look at the Top500 chart [a list of the world’s fastest supercomputers], we made quite a step up,” Hofstee said. “You expect a certain growth rate on the list, but you can actually see that the Cell chip jumped off that quite a bit - we held the record a little bit longer than it’s typically held.”

The system was also incredibly energy-efficient, another benefit of the Cell. Hofstee explained: “We went with this philosophy: instead of turning something off when it’s not needed, turning it on only when it is needed.”

The team would run programs and watch which pieces of the chip turned on. “If we would see a floating point unit turn on when the program wasn’t supposed to have a floating point workload, we would know that something’s not quite right. This is an area where people have made more progress since then, but I really think we were the first to adopt this philosophy.”

Bader concurred: “Up to this point in time, when you needed memory, it would be like going to the store and buying a whole case of food and bringing it back, even if you needed just one can. With the Cell, for the first time, you could take a shopping list, go to the store, and fill up your cart just with the individual cans that you may need, and then come home. That was game-changing.”

But, despite the efficiency gains and its high performance, sales of Cell-powered servers were limited. “It was early technology that lacked the set of programmers and programming tools that were readily available for the processor,” Bader said.

“The programming effort to use Cell required skilled and specially-trained programmers. The real challenge is to produce a radically new architecture that’s more efficient and capable while at the same time having the software co-design with programmers who are ready to take advantage of it.”

Hofstee added: “It was fairly difficult for commercial users to adopt Cell if you knew that you had to write your software in such a way that it would only run on Cell. People have to really take a big leap of faith if you’re asking them to do that.

“We were just a tad too early. There were a number of near misses. For example, OpenCL, the open standard for parallel programming of heterogeneous systems, came just too late.”

Hofstee also believes that one could have taken a compiler from supercomputer manufacturer Cray “and retargeted it to a Cell chip, basically by thinking of the local store as a large vector register file.” At the time, he didn’t think there were any open Cray compilers around, but later discovered the Department of Energy had open-sourced one.

“I wish I had known,” he said. “That would have made it more palatable for a community that just couldn’t make a decision to write their future on the architecture.”

Meanwhile, as server sales struggled, Sony’s core consumer product, the PS3, was also in trouble. Initially sold at a significant loss, the console was costing the company billions, its sales lagged behind Microsoft’s Xbox 360, and developers found the unique architecture difficult to make games for. By 2007, Kutaragi had relinquished active management of the business he had built.

“There were plans to have a second generation Cell which was supposed to have 32 SPEs and four Power processing elements, and scale it up,” Professor Gaurav Khanna told DCD.

“What IBM mentioned is that Sony pulled the funding and there were practical reasons for that - Sony had lost a lot of money, they made a lot of investment, the PS3 didn’t quite take traction as quickly as they’d liked. Without Sony funding the next generation, it just died. That’s the hearsay I have heard.”

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