How Does My Browser Know if a URL Represents a Filename or Directory

Does anyone know what mechanism is used in order for the browser to know if a given URL represents a filename or a directory?

What if any role does the server play in this? And would server participation rely on IIS? In some cases, I understood the server returns some indication if the URL represents a directory, and this causes the browser to append "/" to the URL.

I'm having a serious problem (described here: Relativ开发者_如何学Goe Links with Extension-less URLs), but I can't resolve it because I don't have any idea what the mechanism is that is failing me.

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The server sends a 302 redirect to a /-terminated path.