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I heard almost all parts of Windows are written in C and C++ with some assembly. Why did Microsoft skip C#? Is there any scope for C# in the development of future Windows versions?

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closed as not constructive by tdammers, gnat, BЈовић, Martijn Pieters, World Engineer May 4 '13 at 23:34

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C and C++ compile to assembly. C# compiles to bytecode for the CLI. This bytecode and virtual machine abstraction prevent it from being useable as a language to program an operating system that needs to talk to the hardware directly. Whine in theory, one could write a C# compiler to assembly, the abstractions of the hardware in the associated runtime would still be there making it unsuitable. – user40980 May 4 '13 at 19:49
@MichaelT I thought Windows accessed the hardware through the HAL? If this is the case then the only code which would need to be processor-specific is the HAL itself. – PeteH May 4 '13 at 20:33
I bet they will use Java. Oh and since I am an oracle, I therefore predict they will also rename company to Oracle – gnat May 4 '13 at 20:54
@gnat Microdeck but it won't happen till 2029. Speculation about future actions of organizations or individuals is not constructive. Have a pleasant day. – World Engineer May 4 '13 at 23:35
@MichaelT: C, C++ and C# don't compile to anything. They are programming languages. Programming languages don't compile, compilers do. There are compilers for C and C++ that compile to JavaScript, JVM bytecode, CIL bytecode or LLVM bitcode, for example. There are even interpreters for C and C++. On the flipside, there are compilers for C# which compile to native code, there are also compilers which compile CIL to native code. In fact, there is no implementation of C# in actual use today that does not eventually compile to native code. – Jörg W Mittag May 6 '13 at 11:24

C++ gives you access to the underlying hardware, something C# can't provide. So for the foreseeable future, Windows will be built in C++ (as parts as still built in assembly where raw performance and interrupt handling are necessary).

As a proof-of-concept, Microsoft Research built Singularity, a C#-based operating system. It uses a superset of C# called Spec# and some other extensions to minimize the need for C++ and other lower-level languages.

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of course minimising the need for C/C++ could also be written "still has to use C/C++". – gbjbaanb May 5 '13 at 13:46
@gbjbaanb: The only reason why Singularity still uses C++, C and assembly in parts of the OS is that the OS was being written while Sing# was being designed, and the parts of Sing# that would have been needed to write, say, interrupt handlers hadn't been designed yet when the interrupt handlers were being written. Now that the features are there, one could re-write those parts in Sing#, but Singularity is a research project: showing that it could be written in a managed language is enough, you don't have to actually write it. That's the difference between engineering and research. – Jörg W Mittag May 6 '13 at 11:21
Another big chunk of C++ code in Singularity is the debugging interface, which is in C++ only because it was basically copy&pasted from Windows and .NET, so that the Singularity team could re-use the existing debugging tools. – Jörg W Mittag May 6 '13 at 11:26

In direct answer to your question, I bet you'd find that most of Windows pre-dates C# in any case.

Who's to say what will happen in the future? I've seen so many revolutionary ideas from MS over the last 25 years that I've lost count.

But I read somewhere that VS2012 (the gui at least) was entirely rewritten in C# and WPF, so maybe you could take that as a sign of future direction? But I wouldn't put money on it.

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Not working in product development but clearly microsoft windows for good years will still be developed in C and C + +. This is because the languages ​​allow / provide access to hardware to a safe level instruction. C # runs on MSIL and has no goal of being language OS.

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C# does not "run on" MSIL. C# and all the other .NET languages are compiled to IL, which is basically a hardware-agnostic assembly language. And of course it is also entirely possible to target IL using the C++ compiler, as well. IL is then compiled (JIT or ngen) all the way to machine code for the hardware it is running on. The resulting machine code still has a dependency on the .NET runtime, of course. As of Windows Vista it was possible to write Windows device drivers using C#. So, parts of the OS are in fact written using .NET, but it seems unlikely that the HAL will ever be .NET. – Craig May 5 '13 at 23:00

At the time, there were no serious competitors to C/C++ in systems programming and now it's a legacy codebase that would probably cost a lot to port. C# also did not exist back then. For the record, there are attempts to turn .NET into an OS platform but these are not Microsoft projects.

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There's also a Microsoft attempt called Singularity: and – rwong May 4 '13 at 23:34

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