How does XNA framework 4.0 cross platforms

XNA Framework is an intermediate platform between applications and operation systems. It targets on helping developers to migrate their applications
across multiple operation systems.  XNA Framework 4.0 is dependent on the native implementation of .Net Framework 4.0 on Windows or .Net Compact Framework 4.0 for Xbox. It can be deployed on Windows Phone 7, Xbox 360, and Windows OS (includes
XP, Vista, & Win7). To make the clearance of how it archives that, we can first go to look at the deployment of its binaries.
In here, I installed a XNA Game Studio 4.0 on Win7 AMD64 ENU platform with Visual Studio 2010 Ultimate preinstalled. (You can download XNA
Game Studio 4.0 for free at http://www.microsoft.com/downloads/en/details.aspx?FamilyID=9ac86eca-206f-4274-97f2-ef6c8b1f478f)  

After the installation, we can see a folder “Microsoft XNA” was created in “Program Files” folder. Open this folder and let’s focus on the
location: C:/Program Files (x86)/Microsoft XNA/XNA Game Studio/v4.0/References (take the path on my machine for example). You would see two subfolders in here: “Windows” and “Xbox360”. If we compare the contents of these two folders you may see they contain
quite similar groups of binaries. See table1.
Table1

../Windows/x86/	../Xbox360/
Microsoft.Xna.Framework.dll Microsoft.Xna.Framework.Avatar.dll Microsoft.Xna.Framework.***.dll   Microsoft.Xna.Framework.Content.Pipeline.dll Microsoft.Xna.Framework.Content.Pipeline.***.dll N/A N/A N/A	Microsoft.Xna.Framework.dll Microsoft.Xna.Framework.Avatar.dll Microsoft.Xna.Framework.***.dll   N/A N/A mscorlib.dll System.dll System.***.dll

 
We can see the Windows folder contains a series of “Microsoft.Xna.Framework.Content.Pipeline.dll” related binaries which was not included in
Xbox360 folder. Similarly, Xbox360 folder contains some of “system.dll” related binaries (these binaries are different from those of which have the same name but located in .net framework folders). Additionally, if you compare the same named binaries in above
two columns, you may f
4000
ind they are actually different. Now, you may start to think XNA Framework 4.0 might be trying to provide a uniform named API system. Thus, developers just have to change the referred binaries of the project for platform migration. Let’s
try to find out some evidences for our guess.
 Since we have installed XNA Game Studio 4.0, Visual Studio 2010 now has six brand new project templates
under the type of “Visual C#”->”XNA Game Studio 4.0”.(Pic1) 
Let’s select “Windows Game (4.0)” to create a windows game solution.

Pic1
http://hi.csdn.net/attachment/201101/11/4333508_12947497277y7e.jpg

After the creation you can see the solution has two projects in Solution Explorer. (Pic2)
Pic2
http://hi.csdn.net/attachment/201101/11/4333508_12947500047Cz9.jpg

The first project is the main project named “WindowsGame1”. It has a folder named “Content Reference”. The only element of the “Content Reference”
is the referring of the second project “WindowsGame1Content”. Regardless why we got these two projects, let’s take a look at the references first.
Table2 shows the preset references for both solutions create by template types “Windows Game (4.0) and “Xbox 360 Game (4.0)”.

·        
Binaries highlighted in red refer to .net framework folder. ( C:/Program Files (x86)/Reference Assemblies/Microsoft/Framework/.NETFramework/v4.0/Profile/Client)

·        
Binaries highlighted in green refer to the “Windows” subfolder under the XNA Framework’s references folder. (C:/Program Files (x86)/Microsoft
XNA/XNA Game Studio/v4.0/References/Windows/x86)

·        
Binaries highlighted in yellow refer to the “Xbox360” subfolder under the XNA Framework’s references folder. (C:/Program Files (x86)/Microsoft
XNA/XNA Game Studio/v4.0/References/Xbox360)
Table2

Platform	Windows	XBox
Game references	mscorlib System System.Core System.Net System.Xml System.Xml.Linq   Microsoft.Xna.Framework.dll Microsoft.Xna.Framework.Avatar.dll Microsoft.Xna.Framework.Game.dll Microsoft.Xna.Framework.GamerServices.dll Microsoft.Xna.Framework.Graphics.dll Microsoft.Xna.Framework.Input.Touch.dll Microsoft.Xna.Framework.Net.dll Microsoft.Xna.Framework.Storage.dll Microsoft.Xna.Framework.Video.dll Microsoft.Xna.Framework.Xact.dll	mscorlib System System.Core System.Net System.Xml System.Xml.Linq   Microsoft.Xna.Framework.dll Microsoft.Xna.Framework.Avatar.dll Microsoft.Xna.Framework.Game.dll Microsoft.Xna.Framework.GamerServices.dll Microsoft.Xna.Framework.Graphics.dll Microsoft.Xna.Framework.Input.Touch.dll Microsoft.Xna.Framework.Net.dll Microsoft.Xna.Framework.Storage.dll Microsoft.Xna.Framework.Video.dll Microsoft.Xna.Framework.Xact.dll
GameContent references	Microsoft.Xna.Framework.Content.Pipeline.dll Microsoft.Xna.Framework.Content.Pipeline.AudioImporters.dll Microsoft.Xna.Framework.Content.Pipeline.EffectImporter.dll Microsoft.Xna.Framework.Content.Pipeline.FBXImporter.dll Microsoft.Xna.Framework.Content.Pipeline.TextureImporter.dll Microsoft.Xna.Framework.Content.Pipeline.VideoImporters.dll Microsoft.Xna.Framework.Content.Pipeline.XImporter.dll	Microsoft.Xna.Framework.Content.Pipeline.dll Microsoft.Xna.Framework.Content.Pipeline.AudioImporters.dll Microsoft.Xna.Framework.Content.Pipeline.EffectImporter.dll Microsoft.Xna.Framework.Content.Pipeline.FBXImporter.dll Microsoft.Xna.Framework.Content.Pipeline.TextureImporter.dll Microsoft.Xna.Framework.Content.Pipeline.VideoImporters.dll Microsoft.Xna.Framework.Content.Pipeline.XImporter.dll

 
If we go through the content of the above paths highlighted in green and yellow, we can see that all binaries under their
corresponding paths are referred in the project by default, except “Microsoft.Xna.Framework.Input.Touch.dll” and “Microsoft.Xna.Framework.Content.Pipeline.dll”. We would try to find the reason of this exception in the future. Now, let’s focus on the general
situation.
 
One finding from the table is references of the content projects are the same whatever you are in windows or Xbox game project.
 The other finding is the main projects of windows game and Xbox game are using their own binaries. While windows game project can directly use system assemblies provided by .Net Framework, Xbox game has to provide system assemblies by
itself.
 
Things become clear now. We don’t have a unified framework act as .Net Framework does to allow an application running on
any OS once it has .Net Framework been installed. But, we might be able to code the application once and build multiple applications for multiple platforms with just refer to different series of binaries without much code changes in the project. To approve
our second guessing, we should go into the coding and try to build a project to make the verification, which would be discussed in the next time.