Since the start of E3, complaints of choppy framerates in Halo have been pouring in, with the attendant explanations about unfinished hardware, incomplete optimization, sound emulation, and whatnot. To go with it there's been a healthy dose of confusion and disagreement over a number of things, including the hardware specs of the production Xbox to be released this November, the hardware specs of the Alpha II Xbox Development Kit (XDK) presumably used to demo Xbox games at E3, and what the differences are between them.
Aginor pointed out in Halo.Bungie.org's forum a good article at GameSpot that touches on some of these, focusing particularly on the Nvidia GPU used in the Xbox, specifically about whether the chip was to be the NV20 or an NV25, the chips used in the currently shipping and future versions of the GeForce3 card, respectively. In reality, GameSpot reveals, the chip is an NV2A, custom designed for the Xbox. Based on the NV20, it runs at a faster speed, 250Mhz. Although that's not as fast as the original announced Xbox spec of 300 Mhz, the NV2A does have one more vertex shader pipeline.
There's also been some confusion about the processor. The Xbox's original spec called for a 600 Mhz Intel processor. That was later increased to 733 Mhz. However, there have been reports that people at E3 were claiming the XDKs were using 1 Ghz Pentium IIIs. However, the specs have always just cited An Intel 733MHz processor, the most powerful CPU of any console (specs from Xbox.com and also on xbox.ign.com) without naming the P3 in particular. GameSpot also clears this up, saying the machines at E3 were running at 733 Mhz, just like the production Xboxes will. They also pointed out some of the other differences between the final Xbox and the XDK:
Finally, the preproduction demo consoles Microsoft used to show off Xbox games at E3 didn't include the final audio hardware--Nvidia's MCP chip--to accelerate game sound. Some Xbox developers on the floor explained that the occasional performance slowdowns seen in the games were mostly due to the fact that all audio processing is temporarily being handled by the 733MHz CPU. In the final Xbox, the MCP will handle all of the console's audio processing, networking, and I/O. It's the first chip to take advantage of Dolby's new real-time Dolby Digital encoding algorithm, which will produce true 5.1 game sound for home theater systems.
They also note that because of what Microsoft had to add to XWare-- the special version of DirectX used on the Xbox-- in order to support the second vertex shader, some features will have to be removed from PC ports of Xbox games because DirectX 8 doesn't support it and pre-NV25 GeForce cards don't have it.