My thoughts on recent developer documents from Sony DevStation

Friend and colleague Charlie Demerjian just ran a series of articles detailing some of the hardware used in the development and production Sony Playstation 3.  However, it was Demerjian's piece on memory throughput on the Playstation 3 that sparked everyone's attention.  After having the opportunity to look at the document referenced in the article, I can reasonably confirm that what Demerjian has written is authentic. 

Here is a quick recap of what the DevStation document claims:
  • The original Sony PS3 development kits were configured with a South Bridge between the Cell processor and the RSX GPU. 
  • The RSX GPU has 256MB of local GDDR3 memory, and another 256MB of XDR memory accessible via the South Bridge.
  • The production PS3 systems no longer have a core logic bridge; instead the core logic is integrated onto the RSX package.
  • Cell's read access to the RSX local memory is extremely handicapped -- down to 16MBps.  The write access is still capable of 4GBps.
  • The document goes on to detail the RSX clock frequencies are set at 420MHz with a 550MHz target, and local memory is set at 600MHz with a 700MHz target. 
I will not dwell too much on the South Bridge issue.  With the original development kits, it seemed like it might be a nice feature to use portions of the RSX local GDDR3 to offset the Cell's XDR when needed.  This can still be done by using the RSX as a proxy, but in reality the sense that many applications would even need to read/write to the RSX memory seems unusual anyway.  After all, the whole intention of Cell's SPEs was that the CPU would thread application specific things and the GPU would be ... just a GPU.

The point that makes me irked is the GPU clock and memory speeds.  It was already well known that the RSX was going to be a glorified GeForce 7900 series with an extra trick or two.  Well, the extra trick seems to be the integrated Southbridge, which may help Sony's case in the long run as fewer chips equates to less cost.  550e/700m target clocks are similar to a GeForce 7900GTX.  When the XBOX (the original) launched, the graphics core was sort of a glorified GeForce 3 series GPU, but the whole system cost less than a high end GeForce 3 at the time.  Granted, computing hardware is much more mature than it was in 2001.

Launching with a GPU that is more or less a year old does have some advantages for Sony -- the Xenos GPU featured in the XBOX 360 was new territory for hardware/software developers.  Claiming PS3's 275M triangles per second will be the death of graphics on the PS3 seems like a bit of an overstatement.  I personally have never seen a game push more than 3M polys per frame, which calculates out to 180 triangles per second.  That's not to say the hardware shouldn't push 500M triangles per second as with the XBOX 360, it has to last a few years.

Overall, I suppose I expected a little bit more from SCEE, particularly with the majority of the hype in the direction that PS3 will offset many of the functions of a computer.  It is a high end computer for 2006 with regard to graphics, but expecting something revolutionary may have been setting the bar too high.

"So if you want to save the planet, feel free to drive your Hummer. Just avoid the drive thru line at McDonalds." -- Michael Asher

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