Consortium reveals Cell details, claim 4GHz+ clock speeds

Official details of the Cell microprocessor have been revealed by partners IBM, Sony and Toshiba, with the multi-core architecture set to be capable of processing ten threads on a single chip clocked at over 4GHz.

The chip package will consist of a 64-bit Power processor - similar to the CPUs being used in the Xbox 2 and PowerMac G5 systems - which can process two threads simultaneously, along with eight "synergistic processing units".

These SPUs are the real horsepower behind the chip; each one has 256KB of its own memory and can handle computing tasks separately from the main processor, which will be responsible for dividing up tasks between the SPUs and running the operating system.

While clock speeds are an almost entirely meaningless measurement of processor performance, especially when comparing chips as radically different as Cell and the existing Intel/AMD families, much attention has been focused on the claim that the Cell could start out at speeds of over 4GHz.

Despite not being a clear indicator of actual performance, the speed is still a PR coup for IBM and its partners - since Intel's range of chips currently maxes out at 3.8GHz, while Cell may go as high as 4.6GHz in its early incarnations.

More useful as a performance measurement is the chip's rating in terms of calculations per second, or "gigaflops", with Cell rated at 256 gigaflops according to IBM - a fair bit short of an entry in the Top 500 Supercomputers list, which starts at 851 gigaflops, but still enormously powerful for a single chip, and of course the chips are designed to operate efficiently in clusters.

Indeed, it's widely expected that the PlayStation 3 could boast as many as four Cell chips, which would give a theoretical CPU performance of over 1,000 gigaflops, or one teraflop - a very theoretical measure, admittedly, but still enough to earn the PS3 a place on the supercomputer list.

Another aspect of the performance which IBM has been quick to champion is the memory bandwidth available to the Cell, with the design utilising RAMBUS interface technology that delivers an unprecedented one hundred gigabytes per second of bandwidth to the chip, with separate interfaces for communicating with system memory and with other CPUs.

Despite Sony's claims, one thing we won't be seeing in the near future is Cell being used in portable devices such as mobile phones - according to an IBM spokesperson, the chip, which is initially being manufactured on a 90 nanometre process but will eventually move down to 65 nanometre, runs hot enough to require a cooling fan, like most desktop CPUs.

Spokespeople from the Cell consortium were quick to point out the flexibility of the system, saying that the multi-processor architecture could be used in a variety of different ways by game developers or other software creators.

However, game developers contacted by GamesIndustry.biz downplayed reports that the PS3 would be incredibly difficult to program as a result of the new architecture, saying that the main difficulty would be the move to a multi-core system - a design shared by the Xbox 2 and almost certainly by the Nintendo Revolution.

The game development model which is used for PlayStation 2, where a few programmers work directly with the low level code to create libraries for specific functions and other developers simply use those libraries, masking the complexity of the underlying system, is likely to work just as well on PlayStation 3, while the prevalence of middleware such as Criterion's RenderWare or the Havok physics engine will also make the transition less painful.

Another factor fingered by developers is the fact that Sony's PlayStation Portable libraries and documentation have been widely praised by those working on the system, indicating that Sony has learned an important lesson from the PS2 launch - where much of the development difficulty lay not with the system itself, but with poorly translated (or un-translated) documentation and difficult to use libraries.

Along with the Cell processors, the PlayStation 3 is also set to use a graphics chipset from NVIDIA, which will be based on the company's next generation of GPU, following on from the hugely successful 6000 series of PC graphics cards.