Long long time ago Microsoft produced csc.exe and vbc.exe compilers for C# and VB.NET respectively. Those classic compilers come together with every version of .NET Framework and are usually located at a folder similar to C:\Windows\Microsoft.NET\Framework\v4.0.30319.
The classic C# and VB.NET compilers were written in native C/C++ code to solve the egg and chicken problem when .NET was at the age of infanity.
All Visual Studio versions starting from 2002 used those proven compilers.
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