When does .Net run on UNIX?

I've heard of mono for developing cross platform .Net applications but why does the .Net Framework itself include conditional compilation, for example

#if PLATFORM_UNIX
...
#开发者_Python百科endif // PLATFORM_UNIX

as can be seen in the .Net Framework Reference Source for System.IO.Path

This is for the SSCLI, which uses much of the same codebase and can run on UNIX

I'm going to take a wild guess and go with what you are seeing is relics from Rotor, the FreeBSD implementation of .NET from way back in the day.

IIRC Rotor was somehow related to the conversion effort of Hotmail when MS bought that company.

From the source code of SSCLI, we can figure out the CLR is very easy to support other platforms if MS want to.