The Aspnet_regbrowsers.exe is registration tool which parses and compiles all system-wide browser definitions that are contained browser files into an assembly and installs the assembly into Global Assembly Cache.

In ASP.NET 1.1 the browser information of all the supported browsers was contained in a section called <browserCaps>, where the meta data is in the form XML entries for various browsers.

In ASP.NET 2.0 a new file called .Browser maintains the data of all the browsers in the form xml entries.

We can find the .Browser files of various browsers in the following path:

\Microsoft.NET\Framework\version\CONFIG\Browsers on your system.

These files are complied into an assembly called Asp.BrowserCapsFactory.dll using the Aspnet_RegBrowsers.exe tool.

This allows the server to access the new browser information immediately so you do not have to shut down any of your applications to pick up the information. An application can access browser capabilities through the Browser property of the current HttpRequest.

These are the options provided by the Aspnet_Regbrowser.exe.  

Do not change the predefined browser definition files that come with ASP.NET because service packs might update those files and overwrite your changes.

Application-specific browser definition files can be placed in the application's App_Browsers directory. In both locations, browser definition files must have a .BROWSER file name extension. Using the ASP.NET Browser Registration tool has no effect on application-specific browser definition files stored in an application's App_Browsers directory.

Using the <browserCaps> element in the Web.config file to define browsers is deprecated in the .NET Framework version 2.0, but is still supported. The data in this element is merged with the information from the browser definition files.