ASP.NET 4 includes a number of application folders that are specific to the ASP.NET Framework. In addition to the Bin folder that was a reserved folder in ASP.NET 1.x, the following folders are all reserved in ASP.NET 2.0, 3.5, and 4:
- Bin: This folder stores the application DLL and any other DLLs used by the application. This folder was present in both ASP.NET 1.0 and 1.1. It is also present in both ASP.NET 2.0, 3.5, and 4.
- App_Code: This folder is meant to store your classes, .wsdl files, and typed datasets. Any items stored in this folder are automatically available to all the pages within your solution.
- App_Data: This folder holds the data stores utilized by the application. It is a good, central spot to store all the data stores used by your application. The App_Data folder can contain Microsoft SQL Express files (.mdf files), Microsoft Access files (.mdb files), XML files, and more.
- App_Themes: Themes are a way of providing a common look-and-feel to your site across every page. You implement a theme by using a .skin file, CSS files, and images used by the server controls of your site. All these elements can make a theme, which is then stored in the App_Themes folder of your solution.
- App_GlobalResources: This folder enables you to store resource files that can serve as data dictionaries for your applications if these applications require changes in their content (based on things such as changes in culture). You can add Assembly Resource Files (.resx) to the App_GlobalResources folder, and they are dynamically compiled and made part of the solution for use by all the .aspx pages in the application.
- App_LocalResources: Quite similar to the App_GlobalResources folder, the App_LocalResources folder is a simple method to incorporate resources that can be used for a specific page in your application.
- App_WebReferences: You can use the App_WebReferences folder and have automatic access to the remote Web services referenced from your application.
- App_Browsers: This folder holds .browser files, which are XML files used to identify the browsers making requests to the application and to elucidate the capabilities these browsers have.
The addition of the App_ prefix to the folder names ensures that you already do not have a folder with a similar name in your ASP.NET 1.x applications. If, by chance, you do have a folder with one of the names you plan to use, you should change the name of your previous folder to something else because these ASP.NET 4 application folder names are unchangeable.