XBOX 360

John Savard

I can't really see that as a reason. Yes, the old Xbox is almost like a standard PC, but there are still big enough differences that make it hard for anyone to get Windows running on it:

1) The system timer ticks at a different rate than on a standard PC.

2) IRQ 1 is not buttigned for a (legacy) keyboard but for the USB ports. This might be a problem if Windows expects the legacy keyboard controller is always there, and automatically reserves IRQ 1 for it, without permitting it to be used for anything else. (This was a problem on Linux, at least, and things had to be patched for the Xbox.)

3) The Xbox freezes if you try to probe for the PCI hardware the normal way. (It has been suspected that this is really a hardware bug, but even if it is, a game console doesn't need to have its PCI hardware probed - it is already known what integrated PCI devices there are on the motherboard, and the Xbox doesn't have PCI slots.) This is probably a major showstopper as far as Windows is concerned.

4) There is no BIOS, no INT 13h, nothing. You'd have to write one yourself. (Even though the legacy BIOS is mostly ignored in modern operating systems, and you could write enough code to get NTLDR running, a completely missing BIOS is probably still a showstopper for any hopes to get Windows running. There is likely to be some low-level ACPI-APM-PNP-ESCD related stuff that Windows just needs to be there in order to work.)

5) There is no VGA-VESA BIOS, either - no text mode fonts, nothing. (I'd buttume Windows would need that for displaying the startup screens. I've also heard that the nVidia graphics drivers call the VESA BIOS for certain things.) You would need to write this one yourself, as well.

6) On the Xbox, all video goes out via a video encoder, not through an ordinary RAMDAC. If you change the graphics mode, simply poking the proper timings in the CRTC registers is not enough - the video encoder registers will need to be set up properly as well. You'd probably need to write a custom graphics driver for Windows. (And as nVidia doesn't give out any low-level documentation on their chips, you will not have 3D acceleration. Xbox Linux doesn't have 3D acceleration, either.) Okay, this is not a showstopper as such, but still a tedious task.

There are some other differences and missing bits and pieces as well but they could probably all be handled quite gracefully. The major roadblocks are the missing BIOSes, the PCI probing problem, and (possibly) the IRQ 1. Fixing these things was possible on the Linux side because you have the source and can modify things as you like but you don't have that privilege on Windows.

-- znark