The Graphics System

Specifications of X-Box and PlayStation 2
	X-Box	PlayStation 2
Polygon Performance	300M/sec (untextured)	66M/sec
Sustained Polygon Performance (full features)	100+ M/sec (textured and lit)	20M/sec
Micropolygons/Particles per sec	300M / sec	Not supported
Particle Performance	300M/sec	150M/sec
Simultaneous Textures	4	1
Pixel Fill Rate - No Texture	4.8G/s (anti aliased)	2.4G/s
Pixel Fill Rate - 1 Texture	4.8G/s (anti aliased)	1.2G/s
Pixel Fill Rate - 2 Textures	4.8G/s (anti aliased)	0.6G/s

Built around graphics

A lot of people express doubts with regard to the computing power of the X-Box - after all, a 600MHz P3 is middle of the road performance even today. What's it going to be worth over a year from now? Why marry yourself to anything less than a gigahertz chip? The answer might be that the CPU won't be shouldering most of the load. Microsoft is supremely confident in the graphics capability of the X-Box. During the GDC keynote, Bill Gates proclaimed that the graphics chip would do 1 trillion operations per second. Remember the 3dfx Voodoo 3 commercials proclaiming 100 billion operations per second? A trillion is a full order of magnitude better than that. Some other numbers to get your juices flowing - 467 floating operations per clock. At 300MHz, that translates to about 140 gigaflops of performance!

More polys than you can shake a stick at

The Playstation 2's polygon performance, at 66M/second is already very impressive. But Microsoft is now saying we should expect to see the X-Box do as many as 300 M polys per second, with a sustained rate of over 100 million a second. *Cough* Pardon us for being skeptical, but this is many times over and above what NVIDIA's current hardware is capable of. With not much more than a year to go before X-Box needs to be on store shelves, we'd have to say that 300 M polygons per second might be very wishful thinking. Not to say that it's totally out of the question, but we'd be pleasantly surprised to see X-Box hit the mark on this front.

It's all about the fill rate

We see from the numbers that the X-Box will fill at a very impressive 4.8 gigapixels per second! This is about twice as much as the Playstation 2, 4 times higher than the Voodoo 5 6000's projected performance, and 6 or 7 times higher that what the NV15 is expected to output when it's released. And unlike the Playstation 2, the performance doesn't degrade after adding one or two textures; this gives the X-Box graphics processor almost a 10 gigatexel fill.

Clock speed is key

But wait a second - the clock speed is "only" 300MHz! 4.8 gigapixels/300MHz = 16 pixels per clock. Does this infer a monstrous 16 pixel pipeline? It sounds outrageous now, but with current top end video cards giving a quad pixel pipe, it's not totally out of the question. There is another thing to consider as well. A wider pixel pipeline means even greater importance placed on the clock speed of the graphics chip. A 50MHz drop in the clock speed of a GeForce card means a 200 megapixel loss in fill rate. The same drop in clock speed of the X-Box would spell a nearly gigapixel (800 megapixel) loss in fill rate though! This presents another pitfall of early numbers - if NVIDIA can't hit the projected clockspeed of 300MHz (remember, there's precedent here with the TNT and TNT2), then these fillrate numbers go straight down the tubes. Time will tell.