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.
"If they're going to pirate somebody, we want it to be us rather than somebody else." -- Microsoft Business Group President Jeff Raikes
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