Assembly question

Last October I posted a question on BigIntergers : http://social.technet.microsoft.com/Forums/windowsserver/en-US/57f6150f-0ef1-4299-b86f-633b93dfe1ee/systemnumericsbiginteger-bug-or-no-bug-?forum=winserverpowershell

I'm trying to have a better understanding about the different Assemblies. In my post from October, I use Add-Type -Path "C:\Windows\Microsoft.NET\Framework\v4.0.30319\System.Numerics.dll" to load the assembly. I've found this on the Internet, but how can I find the information myself ?


Here are my step so far:
1. Going to http://msdn.microsoft.com/en-us/library/system.numerics(v=vs.100).aspx - There I can see all the .NET Framework Class Library
2. I select System.Numeric
3. The missing  step ! Where can I find out in which DLL is the System.Numeric NameSpace ?  Is there a document showing the Path of the DLL ? or should I make the assumption that the DLL will always be located under C:\Windows\Microsoft.NET\Framework\v4.0.30319

So for instance if I want to load the System.Media Namespace, which DLL should I load ? and Where I can find the information ? FYI: I do not see any System.Media DLL in the C:\Windows\Microsoft.NET\Framework\v4.0.30319 folder

If anyone, could also explain to me what is the difference between an Assembly and a Namespace, that will also help

Thank you for your help & Happy New Year 2014