RSX 'Reality Synthesizer'

The RSX 'Reality Synthesizer' is a proprietary graphics processing unit (GPU) codeveloped by Nvidia and Sony for the PlayStation 3 game console. It is a GPU based on the Nvidia 7800GTX graphics processor and, according to Nvidia, is a G70/G71 (previously known as NV47) hybrid architecture with some modifications. The RSX has separate vertex and pixel shader pipelines. The GPU makes use of 256 MB GDDR3 RAM clocked at 650 MHz with an effective transmission rate of 1.4 GHz and up to 224 MB of the 3.2 GHz XDR main memory via the CPU (480 MB max). Although it carries the majority of the graphics processing, the Cell Broadband Engine, the console's CPU, is also used complementarily for some graphics-related computational loads of the console.

Unless otherwise noted, the following specifications are based on a press release by Sony at the E3 2005 conference, slides from the same conference, and slides from a Sony presentation at the 2006 Game Developer's Conference.

Other features: Support for Bilinear, trilinear, anisotropic, quincunx texture filtering, quincunx antialiasing, up to 4xMSAA, SSAA, Alpha to Coverage and Alphakill.

Although the RSX has 256MB of GDDR3 RAM, not all of it is usable. The last 4MB is reserved for keeping track of the RSX internal state and issued commands. The 4MB of GPU Data contains RAMIN, RAMHT, RAMFC, DMA Objects, Graphic Objects, and the Graphic Context. The following is a breakdown of the address within 256MB of the RSX.

Besides local GDDR3 memory, main XDR memory can be accessed by RSX too, which is limited to either:

System bandwidth (theoretical maximum):

Because of the aforementioned layout of the communication path between the different chips, and the latency and bandwidth differences between the various components, there are different access speeds depending on the direction of the access in relation to the source and destination. The following is a chart showing the speed of reads and writes to the GDDR3 and XDR memory from the viewpoint of the Cell and RSX. Note that these are measured speeds (rather than calculated speeds) and they should be worse if RSX and GDDR3 access are involved because these figures were measured when the RSX was clocked at 550Mhz and the GDDR3 memory was clocked at 700Mhz. The shipped PS3 has the RSX clocked in at 500Mhz (front and back end, although the pixel shaders run separately inside at 550Mhz). In addition, the GDDR3 memory was also clocked lower at 650Mhz.

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