Silverlight Architecture
Unlike ASP.NET, the bulk of Silverlight processing occurs on the client machine thus decreasing server resource utilization and improving the Web experience on the client. The figure below shows the difference between ASP.NET processing and Silverlight processing:
When a client initially attempts to run a Silverlight application, if the Silverlight plug-in has not been installed on the client machine, it will be downloaded and installed. Upon subsequent requests to run the application, the application will instantiate on the client machine and make requests for resources from the server only when necessary. The Silverlight plug-in can be thought of as a scaled-down version of the full .NET Framework. It only contains those classes and functionality that are applicable to a Silverlight Web client and those were streamlined and optimized for use on the Web client machine.
Silverlight was designed using the same design paradigm as ASP.NET. Each page of a Silverlight application includes an associated code behind file that includes the code that handles events fired by the page. Silverlight resembles WPF in that it uses Extensible Application Markup Language (XAML) to construct the user interface (presentation layer). As Silverlight applications are composed of text-based files that include markup and code, they can be created using any text editor; however, more advanced tools and development environments such as Visual Studio or Expression Blend simplify the task significantly.
Silverlight Technologies
Version 1.0 of Silverlight used JavaScript and supported the industry-leading Windows Media Services enabling delivery of audio and video that includes 2D and vector graphics.
Version 2 includes all features of version 1.0 and:
- support for the .NET Framework.
- support for .NET-compliant programming languages such as C#, Visual Basic, Python, and Ruby.
- support for database operations and language-integrated query (LINQ).
The figure below illustrates the major differences between version 1.0 and version 2: 
The diagram located at ClassFiles/WhatIsSilverlight/Demos/SilverlightTechnologyMap.gif gives a broad picture of the technologies to be supported by Silverlight version 2.
Silverlight Hosting
Microsoft Silverlight functionality is completely encapsulated within the Silverlight plug-in. Web applications typically require the server hosting the Web application to meet minimum requirements. Silverlight applications simply require a Web server to be equipped as they would be for hosting HTML documents. Silverlight applications can be hosted on any Web server accessible to the target audience. The two most commonly used Web servers are Microsoft Internet Information Server (IIS) and Apache.
Executing a Silverlight application on a Web client machine is a two step process. First, the application will detect if the Silverlight plug-in is installed on the Web client machine. If the plug-in is not installed, the user will be prompted with an option to download the plug-in. If the user opts to do so, a request will be made of the Web server to download and install the plug-in. The Silverlight plug-in is embodied in a .dll executable file that is loaded into the Web client browser memory once installed. The only interaction required by the Web client when installing the Silverlight plug-in is to grant permission for the plug-in to be installed. Various Web servers, including Microsoft Internet Information Server (IIS), may require slight configuration modifications so that the Silverlight executable file will be downloaded to the Web client when requested.
Second, once the Silverlight plug-in is installed on the Web client machine, the Silverlight application itself must be downloaded. A Silverlight application may consist of many types of files. Slight configuration modifications may be necessary on the Web server, such as MIME types, so that XAML and XAP files are associated with Silverlight and downloaded correctly to the Web client machine when requested.
Once the Silverlight plug-in is installed on a Web client machine and a Silverlight application is downloaded, the Silverlight application is then hosted on the Web client machine. There are some requirements necessary for the Web client machine as discussed in the sections below, however all media players, audio and video codecs, compilers and the runtime are encapsulated in the Silverlight plug-in.
Supported Platforms
Silverlight can be installed on Windows and Macintosh machines. Silverlight applications run within the confines of a plug-in. There are many benefits to using a plug-in with the primary benefit being consistency across implementations. A plug-in application can provide a consistent result in every instance where it is supported. Other plug-in solutions, such as Adobe Flash, have become popular due to consistency across implementations. For instance, a plug-in application should deliver a consistent result regardless of whether it is displayed using Internet Explorer on Windows or Safari on a Macintosh.
Silverlight 2 is currently supported on the platforms discussed below. (see footnote)
| Platforms that Support Silverlight 2 | |
| Operating System | Browser |
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