[quote name='eros']If Microsoft is going with ATI for the graphics card than, yes, the XBox2 will not be backwards compatiable period.
Even if they manage to emulate the XBox 1's other functions in real time on the XBox 2. Because of IP rights of nVidia, with respect to the graphics unit it won't happen. And if you don't think nVidia will scream bloody murder and drag MS to court and delay things, if they try such a thing, you're nuts. Afterall, ATI is nVidia's sworn enemy, and MS siding with them is going to piss them off. And no matter how much money MS has, I'm sure nVidia's lawyers could find a way to drag the release thing out for a year or two.
The other thing with the XBox 2 is the new APIs that MS is pushing on everybody -- XNA. A lot of developers still do cross-platform developement and if a developer decides to use XNA, the ability to be cross-platform isn't going to happen. And what with XNA being developed in house you can bet that when the XBox 2 comes out a developer will have three choices:
1) Roll his own code. Costly and timely.
2) Use XNA, and forget about releasing for another platform other than PC or code everything twice.
3) A bunch of costly third party solutions that won't be as finely tuned as MS's XNA for a few years.
All and all, if XBox 2 releases first with no backwards compatiability, no hdd, and pushing XNA, they are going to bleed billions like they have on this generation of XBoxes. We will see how long Bill and the stock holders will allow this to go on.[/quote]
I just wanted to point out that while I'm sure you had good intentions when you wrote this post, technically it is wrong.
Libraries such as DirectX and XNA (still unclear what XNA really is) are only beneficial to software developers. Instead of having to worry about how to fill in a triangle on the screen, developers can just say "draw triangle" and some code that has been debugged and tested massively by all the other developers before you will do the job for you with small to zero chance of failure. Of course this is a simple example but I would much prefer developers to spend their time working on GAMES rather than low level boiler-plate code.
The cross platform issue - if you are developing a cross platform product and have properly structured your code architecture it doesn't matter what APIs you are using at the base level. Say you create your "Enemy" class which works on both the Xbox and PS2 since it is standard C++. The drawing code though is hidden via abstraction - who cares if you use XNA on the Xbox and the DMAC on the PS2? That part is hidden from your game and that is the whole point of building something that will work cross platform. No need to worry about Microsoft providing additional APIs to get rid of cross platform games. This is how cross platform development works now and always will work. Microsoft paying developers to make things exclusive though, that is another story ;-)
As for the ATI / nVidia backwards compatability issue - it is really a non issue. You seem like you know that the Xbox and PC architecture are very similar - but did you know the Xbox uses DirectX? Changing the graphics card inside the box would be like changing it in your PC - all of the games are coded against DirectX - so if Microsoft plugged in a new driver for their new ATI card on the motherboard all games would run the same old code base and they would work automatically. This is the purpose of DirectX's existence. IP rights are not violated - ATI isn't stealing nVidia's architecture. The nVidia chip is simply being replaced.
Now, the CPU based proposition of Intel vs. RISC is really the best indication of no backwards compatability of course. I actually doubt current Xbox games could be viably emulated even given the prospective specs of the next system. Emulation is just slow - my current near top of the line PC can't emulate PS1 games smoothly in all cases. I think I read a postulation somewhere that to emulate a system completely the emulator must be approximately 10 times as powerful as the previous system. Who knows if that is true but it is clear Xbox 2 is not 10 times as powerful as Xbox 1.