Silverlight and the full-featured .NET Framework are two different things that tend to be common. The version numbers of them become even more confusing, but here goes ...
Silverlight 1 , .
Silverlight 2, 3 4 , "2.0.5.0" (System.dll, System.Core.dll ..). "5" : "S" Silverlight, "2.0.0.0", .NET Framework. , Silverlight .NET Framework, , DLL, , 2.0.0.0 " API Foo", API Silverlight - , 2.0.5.0 "" ".
Silverlight CLR, "CoreCLR", .NET Framework "CLR". CoreCLR CLR ( Mac, ). Silverlight 2 3 CoreCLR 2, CLR 2 ( .NET Framework 2-3.5). Silverlight 4 CoreCLR 4, CLR 4 ( .NET Framework 4).
, Silverlight Windows Phone 7 .NET Compact Framework, CLR CLC (CLC NETCF).
, , , Microsoft " Portable Library" (. http://blogs.msdn.com/b/bclteam/archive/2011/01/19/announcing-portable-library-tools-ctp-justin-van-patten.aspx), , ".NET-" ( .NET, Silverlight, Windows Phone, XNA XBox 360, , , Mono), .
, , .
, - " .NET 4 Silverlight", CLR .NET 4, Silverlight 4. , , , Silverlight 4.