http://www.c-sharpcorner.com/UploadFile/yougerthen/what-really-make-difference-between-structures-and-classes/

http://msdn.microsoft.com/en-us/library/hh191443.aspx

The await keyword is syntactical shorthand for indicating that a piece of code should asynchronously wait on some other piece of code. The async keyword represents a hint that you can use to mark methods as task-based asynchronous methods. The combination of await, async, and the Task object makes it much easier for you to write asynchronous code in .NET 4.5.