So we can visualize the silver light architecture as combination of some functionalities from core .NET framework , Ajax and some functionalities like animation , media etc provided by core silver light framework.
•.NET framework components: - Silver light uses some components from .NET framework. One of the main components is WPF. Many of the UI components (check box, buttons, text boxes etc), XAML parsing etc are taken from the core WPF system. It also has taken components like WCF to simplify data access. It also have CLR for memory management, safety checking and garbage collection. The base class libraries of Net are used for string manipulations, algorithms, expressions, collections and globalization.
• Presentation core: - The core presentation framework has functionalities to display vector 2d animations, images, media, DRM and handle inputs like mouse and keyboard.
See following for detailed information here:
Difference between Silverlight Runtime and Silverlight SDK
Silverlight Runtime is a plug-in for browsers to support Silverlight enabled applications. If Silverlight runtime is not installed, browsers will not be able to run Silverlight elements in the browser. You can set up your Silverlight tags such a way that your browser will automatically prompt the user to download and install the Silverlight plug in when your application is launched in the browser.
Installing the run time is a onetime operation on the client. Once installed, it will be automatically launched when any Silverlight application is loaded in the browser.
Silverlight SDK is a set of tools, documentation, samples and templates for the web developers to help them easily develop Silverlight enabled applications. The SDK is not really mandatory to develop Silverlight applications; however, SDK will make development much easier.