Confirmation on X-Box 360's OS?

[benjamin]

Last I understood the X-Box 360 was using a customized OS and kernel. Question is, to what extent is it derived from the NT/kernel source (if at all)? My understanding was that it was not nearly as derived as the first XBox's OS.

Any confirmation of this?

 

[Shifty Geezer]

I was of the impression it is certainly a derivative. It uses the same XNA APIs and is to work as a media hub in conjunction with your 'media PC'. Cut down perhaps, but not radically different, surely?

 

[Glonk]

It is a derivative of the Xbox OS, which is a derivative of Windows 2000's kernel.

 

[Shifty Geezer]

No Longhorn presence at all?

 

[BlueTsunami]

I remember a while back hearing something about XBox 360 using some features of Longhorn...I wonder what happened with that? I think it will be dissapointing if all they use is a upgraded version of the XBox's OS interface...

 

[benjamin]

I think the more interesting thing is what if any changes are being made to the kernel (if any), and what OS or API support will look like with regards to the programmatic L2 streaming read/write modes, etc.

 

[shaderguy]

You don't need any kernel or OS changes to support programmatic L2 streaming. The PowerPC instruction set has instructions for flushing, loading, and clearing cache lines. So all you need are very simple intrinsics in your C/C++ compiler. (Or you can just use inline asm).

As for OS changes, why would they need to change anything? Microsoft has had the NT kernel running on the PowerPC architecure since the PowerPC first came out in the 90s. Like Linux NT is totally portable to basicly any CPU architecture that has kernel mode. (And like Linux it's used 99% on Intel hardware, but that's due to the cost benefit of Intel hardware, not any inherent portability problem in the OS.)

Actually, since NT was originally written for the i860 (a RISC machine), and then ported to the x86, it's likely to be even easier to port than Linux.

 

[benjamin]

I'm aware of NT's architectual history, I wasn't referring to porting it to a new ISA.

But thanks for answering my question of how to interface with the L2 cache options.

As far as changing the OS/kernel, I am referring to upcoming kernel changes for display drivers in Longhorn. Was there ever a CPU cost on the XBox when switching between kernel/user mode when calling DX functions? If so, that is one possible change in the new XBox 360 OS build.

 

[Rockster]

Yeah, I would be interested in that as well. Longhorn + WGF2.0 supposedly greatly reduces driver overhead from drawprimitive calls, etc.

Seems to me though, since the OS and drivers are unique to each game, these features could come later via an SDK update.

 

[benjamin]

Here we go, going by this, the new OS has non trivial modifications from the previous XBox OS:

http://www.windowsfordevices.com/news/NS3988467635.html

 

[arhra]

As far as changing the OS/kernel, I am referring to upcoming kernel changes for display drivers in Longhorn. Was there ever a CPU cost on the XBox when switching between kernel/user mode when calling DX functions? If so, that is one possible change in the new XBox 360 OS build.

Everything runs in kernel mode on the xbox, so calling a DX function is just a direct function call. There's not a lot of use for kernel/userspace seperation when you're just running a single process...

 

[benjamin]

Is that still the case when running XBox live?