Xbox 360 and PS3, the CPU story

I've repeatedly called the PS3's Cell the more powerful processor out of the two when compared to the 3-core PPC chip in the 360. I've also said that the difference in real world performance between the two chips may be very different from the on-paper performance differences.

The strength of Cell is truly derived from its SPE array; with reference to 3D graphics and gaming, we've long since known that two things result in the best performance: lots of bandwidth, and specialized hardware. All of the previous generation consoles implemented (in one way or another) these fundamental principles of making stuff fast. At the same time, PCs always caught up by, at first, embracing the GPU and then by simply increasing general purpose CPU speed by leaps and bounds from one year to the next.

The 3-core PPC processor in the Xbox 360 is no slouch either. Remember that just one of these cores, regardless of its clock speed, isn't exactly the most powerful core on the market. But being relatively narrow 2-issue cores, if you stick a bunch of them together you get something fairly powerful - especially if the applications you're running on them are properly multithreaded.

The main difference between these two CPUs is the general purpose vs. specialized hardware approach. If the goal of either of these consoles was a machine that could run any application well, then the 360 has the upper hand. You don't really see people running MS Office on their MPEG-2 decoder chips. But, if you're talking about tons of physics calculations, 3D calculus and other complex floating point math, similar to what's required in video decoding as well as 3D gaming, then specialized hardware will always give you better performance. To use the MPEG-2 decoder example, there's a reason why video decode and encode assist was pulled off of general purpose CPUs in PCs as fast as possible - there are some things that can simply be done better with specialized silicon. We saw another example of this with the move to the GPU and away from CPU based software rendering of games. Ageia's announcement of the PhysX PPU also echoed the need for specialized hardware when dealing with the complex physics and AI modeling that must be done for the next generation of 3D games. It is because of the Cell's extensive use of specialized hardware that I refer to it as the more powerful processor, on paper.

The distinction "on paper" is particularly important because a lot of the performance debate will really come down to two things: 1) how much processing power will be needed for the next generation of games, and 2) how much of it will be taken advantage of on Cell.

Tim Sweeney made it a point to mention that their Unreal 3 tech demo (which was rendered in real time) only took two months of work on the PS3 hardware they received. The sheer number of demos and quality of demos that were shown off at the press event leads me to believe that the PS3 isn't impossible to program for (given that all developers should have had similar amounts of time with the dev kits). But the question isn't whether or not the PS3 will be impossible to develop for, it is how much of its power will be used.

The first hurdle is obviously getting game developers to multithread their engines. This is a much bigger hurdle than optimizing for Cell or the 360's 3-core PPC processor. I have a feeling that it may take a while before we see properly multithreaded game engines running on consoles (the current estimate is year-end 2006 for multithreaded game engines to appear on the PC), so the first generation of games for the 360 and PS3 may end up being more of a competition of GPU horsepower. From what I've seen thus far, the demos that are being showcased aren't really focusing on the physics or AI aspects of what these next-generation consoles can do, rather mostly focusing on the fact that we finally have consoles with GPUs powerful enough to render scenes at 720p or 1080p resolutions.

Some of the PS3 demos did show off the rag doll physics but nothing appeared to be any more complex than what we've already seen in Half Life 2.

If that is the case, and the first generation titles aren't really well multithreaded then the performance argument for Cell begins to fall apart. The question then becomes whether or not its performance potential will be truly seen during the lifetime of the console. I have a feeling it will, but I'm not much of a fortune teller.

So when will PCs catch up? The console vs. PC debate has always been a balance, consoles would always debut more powerful than PCs, then PCs would catch up and surpass consoles during their ~5 year lifespan. The difference this time around is that the desktop CPU industry is going through a big of a transitional period, it may take a little longer than usual for desktop CPUs to be able to outclass (in all areas) their console counterparts. As far as GPUs go, by the end of this year I'd expect to see 360 and PS3 class (or faster) GPUs offered for high end PCs. By the time the PS3 is released, I would say that the upper mid range GPUs will offer similar (or very close) performance.

The truly limiting factor will be the transition to 65nm on the desktop, the faster that can happen, the quicker the PC will regain its power advantage. But despite any power advantage, this next generation of consoles will definitely be powerful enough to tempt away some PC gamers...at least for a while.