The south bridge (which uses standard interfaces, including the PCI Express link between it and the GPU) handles the comparatively low-speed peripherals. Serial ATA (SATA) interfaces are used for both the hard disk and optical drive. And, the USB interfaces with handheld gaming controllers.
The PlayStation 3 architecture resembles the Xbox 360 at a very high level. The major difference is that the PlayStation 3's Cell processor is the center of its world, while the GPU is the center of the Xbox's architecture (see "More Cores" online at Drill Deeper 12553). The biggest change is that system memory is connected directly to the Cell processor.
Rambus was instrumental in designing the interfaces to the Cell processor. They include the 64-bit, 25-Gbyte/s memory interface, the FlexIO used to link the Cell processor to the IO bridge (which is comparable to the Xbox 360's south bridge), and the GPU. The protocol-agnostic, parallel FlexIO runs at speeds up to 8 Gbits/s. Sony isn't providing details about the interface, though it really doesn't affect application programming. Also, audio support in the PlayStation 3 resides in the GPU rather than the I/O bridge (see "The Sound Of Thunder" online at Drill Deeper 12554).
WHAT YOU SEE IS... ATI's and nVidia's VPU chips for the Xbox 360 and PlayStation 3 are custom versions of the graphic architecture used in PC video adapters. The GPU architecture from nVidia exposes the general layout for high-performance GPUs (Fig. 5). At a high level, nVidia's architecture is similar to ATI's. Application programming interfaces (APIs) used by game developers, like Microsoft's DirectX, hide the underlying hardware and convert a 3D virtual world into a 2D presentation screen
One major difference between GPU and CPU design is that GPUs typically have numerous processors, longer pipelines, and a very regular architecture. This is possible due to the GPU's very structured environment. For example, long pipelines in a GPU usually don't deal with flushing. However, a CPU's pipelines often will flush when a branch occurs. In this sense, GPUs tend to be closer to DSPs that are designed for efficient, repetitive computation.
One prevailing trend in GPUs involves the migration from integer to floating-point encoding. With extremely high-dynamic-range operation that includes floating-point support, more details can be integrated in the dark areas of an image, as well as in the brighter areas. This more closely matches the human eye's response, creating a more realistic experience.
Though ATI's approach differs slightly from nVidia's, the company still has dedicated groups of processors for vertex and pixel processing. Also, the data flow through the system is very wide, and processing is highly parallel in nature. What changes are the details of how each stage are tied together and the type of processing employed in areas such as pixel shaders.
Gamers with big bucks looking for the ultimate visual feedback can check out nVidia's SLI (Scalable Link Interface). SLI uses multiple GPUs to increase performance. It can split the processing burden in various ways, depending on the number of GPUs supported (Fig. 6).
Dual configurations support split-frame-rendering (SFR) and alternate-frame-rendering (AFR) modes, while a four-GPU system also supports AFR or SFR mode. ATI's Crossfire technology is similar in functionality to nVidia's SLI. Both companies require a motherboard to handle their cards.
SLI is applicable to PCs, but not to fixed-architecture console games. Trying to pick the best or fastest architecture is very difficult due to the many factors involved, including the type of games being considered and how they're designed.
LAWS OF PHYSICS The vase drops and breaks into hundreds of pieces. A cluster bomb destroys half a dozen space cruisers. Water flows slowly down a creek while a little minnow flips out of the water and flips back in with a splash. All of these images have one thing in common—physics.
Like 3D hardware graphics acceleration, Ageia's PhysX PPU ($299 MSRP) brings real physics to game play. The challenges addressed by 3D graphics hardware and physics acceleration hardware are complex and require lots of calculations. But streamlining the process and providing a standard interface has made both practical options for a wide range of games. In the future, the best performance of high-end games will only be revealed when physics hardware support is available, such as 3D graphics.
PhysX and 3D gaming have much in common. Both maintain the state of the environment, and the application on the CPU changes the environment by providing transformation information. That's a small amount of information compared to the environment and number of calculations required to apply the transformation.
Also, like 3D graphics, Ageia's physics environment is parametrized to simplify and standardize interaction between the application and the hardware. For example, cloth is a type of item within the physics environment that is defined by 12 different parameters like texture and flexibility
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