Windows x64 and the Microsoft .NET Framework: 32-bit or 64-bit?

The Microsoft .NET Framework is the core “runtime” and libraries for all Microsoft .NET applications.  On Windows x64, the Microsoft .NET Framework v1.1 will run as a 32-bit application – not as a 64-bit application.  In the next release of .NET, the installer will install a native x64 version of the .NET framework, along with a 32-bit version (yes, TWO identical .NET Frameworks – one x64 and one 32-bit).  To understand why Microsoft is doing this, let me explain how .NET applications really “work”.

 

When a developer is finished writing his application, he uses a .NET enabled compiler to compile his code into a .NET assembly (usually into a .exe or a .dll file).  A .NET Assembly does not contain any architectural “machine” code, it contains “MSIL” – Microsoft Intermediate Language.  When you run a .NET assembly, the .NET “CLR” – Common Language Runtime reads the MSIL and converts it into code that your architecture can understand. 

 

With this in mind, why doesn’t .NET 1.1 run assemblies as an 64-bit process on Windows x64?  The quickest answer would be, .NET 1.1 simply does not have any type of x64 support.  So why not make a patch, or release an update to .NET 1.1 to make it support running 64-bit assemblies? 

 

The answer is compatibility.  In .NET, a developer can still use COM controls and make Win32 calls in their assemblies.  A 64-bit application can’t host 32-Bit COM controls, and if you ran an assembly in 64-bit mode – it would have a problem if it made a 32-bit specific call.

 

In the next release of .NET, .NET 2.0, Microsoft will include x64 binaries and 32-bit binaries in the x64 setup.  Microsoft also has added a new setting to the various .NET Compilers which determines which architecture you want your assembly to target – 32-bit, x64, IA64 (Itanium), or “anycpu”.  If a developer specifies 32-bit, the application will run as a 32-bit application on Windows x64.  If the architecture is set to “any cpu”, it will run on any .NET supported platform (providing it doesn’t use any architecturally specific calls).

 

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43 responses to “Windows x64 and the Microsoft .NET Framework: 32-bit or 64-bit?

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