what is "Loading symbols" and why does it take so long the first time?

c#, visual-studio-2012, web-applications

Solution

I believe you can disable it via

 Tools -> Options -> Debugging -> Symbols
 check Automatically load symbols

and

 Tools -> Options -> Debugging -> General
 enabling "enable Just My code "

Problem

When I first execute my C# Web Application project from Visual Studio 2012, the first launch always takes quite a while, usually 20 to 30 seconds. Most of this time seems to be "Loading symbols for reference X.Y.Z.dll". Each of my around 30 references takes about a second to load these symbols. Once they've been loaded the first time, it usually only takes a few seconds for subsequent executions. What is this "loading symbols", exactly? Why does it take so long? Is there a way to speed it up?

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