The revision bumps up the IBM "Gekko" CPU's speed from 405MHz to 482MHz, while decreasing that of the ATI "Flipper" graphics chip from 200MHz to 162MHz. Greg Buchner, ATI's vice president of engineering, told GameSpot that the primary reason for the change was to better balance the system and respond to game developers' wish for a faster processor. The decrease in Flipper's speed isn't related to problems with getting it to run at that speed but is instead due to the fact that the CPU needed to run at an integer multiple of Flipper.
The balance Nintendo decided on uses a multiple of three instead of the planned multiple of two. While many PC systems can use half-step multiples, Buchner said that this approach--which might have more flexibly allowed for a multiple of 2.5 between Gekko and Flipper--wasn't technically possible in this case.
Despite some speculation to the contrary, Flipper does not use any technology related to ATI's recent announcement of Truform, which will let the company's next-generation PC graphics chip boost polygonal detail in existing games by a factor of 10.
Flipper was developed from scratch after Nintendo and ArtX signed a deal back in 1998. ATI acquired ArtX in April of last year, but nearly all of Flipper's design had been finalized by that time, which happens to be about when Nintendo started providing the first development kits to GameCube developers. The ArtX designers from the Flipper team have long since started work on future ATI high-end desktop graphics chips. ArtX's other team, which developed an integrated graphics chipset with ALi, is working on ATI's upcoming chipset based on the Radeon graphics core that will compete with Nvidia's just-announced nForce.
The key to the GameCube's performance is the way it uses embedded memory for low latency and high bandwidth. The 3MB of memory on Flipper accounts for about half of the chip's 51 million transistors, and the on-chip design allows for more than 20GB/sec of bandwidth, although bandwidth drops to 3.2GB/sec when textures are stored in main memory. The Flipper rolls up nearly all non-CPU tasks onto a single chip, including the memory controller for the 24MB of main memory and 16MB of secondary memory, which some developers are using much like a traditional cartridge's ROM to cache priority data stored on the comparably slow optical game discs.
As Nintendo showed off many of the biggest GameCube launch titles a few weeks ago at E3, it's natural to ask what hardware potential remains to be unlocked by games much further from release. Buchner pointed to the Flipper's advanced texturing system as one place where there's room to grow, as developers learn to best take advantage of the up to eight simultaneous textures supported by the GameCube. The high number of textures per 3D surface enables developers to use more complex lighting, shadowing, and environmental mapping effects. While it may take more than one clock cycle to do the extra effects, the chip's design may seem much like a single pass process, since it isn't necessary to resend 3D geometry and associated data to the chip to complete the calculations.
There are still quite a few details that ATI can't reveal about the technology in the GameCube, but there should be more announcements about two months from now. Flipper's anti-aliasing capabilities have been confirmed to use multisampling techniques--presumably like the quincunx method in the GeForce3 and the Xbox--instead of less efficient supersampling. Buchner commented that there's "a lot of magic in there" and that ATI has filed for patents in this area, but there is some performance hit as a result.