ASP.NET supports two modes of page development: Page logic code that is written inside <script runat=server> blocks within an .aspx file and dynamically compiled the first time the page is requested on the server. Page logic code that is written within an external class that is compiled prior to deployment on a server and linked “behind” the .aspx file at run time.

The free subroutine frees a block of memory previously allocated by the malloc subroutine. Undefined results occur if the Pointer parameter is not a valid pointer. If the Pointer parameter is a null value, no action will occur. The realloc subroutine changes the size of the block of memory pointed to by the Pointer parameter to the number of bytes specified by the Size parameter and returns a new pointer to the block. The pointer specified by the Pointer parameter must have been created with the malloc, calloc, or realloc subroutines and not been deallocated with the free or realloc subroutines. Undefined results occur if the Pointer parameter is not a valid pointer.

By using Visual Studio, .NET Framework and WSE, we can quickly build Web services and client applications that can communicate and interoperate with Web services and client applications running on other operating systems. So why do we need WCF? Well, as we have already seen, Web services are just one technology that we can use to create distributed applications for Windows. Others already mentioned include Enterprise Services and .NET Framework Remoting. Another example is Microsoft Message Queue (MSMQ). If we are building a distributed application for Windows, which technology should we use, and how difficult would it be to switch later if we need to?
The purpose of WCF is to provide a unified programming model for many of these technologies, enabling us to build applications that are as independent as possible from the underlying mechanism being used to connect services and applications together (note that WCF applies as much to services operating in non-Web environments as it does to the World Wide Web). It is actually very difficult, if not impossible, to completely divorce the programmatic structure of an application or service from its communications infrastructure, but WCF let us to come very close to achieving this aim much of the time. Additionally, using WCF enables you to maintain backwards compatibility with many of the preceding technologies. For example, a WCF client application can easily communicate with a Web service that you created by using WSE. If we are considering building distributed applications and services for Microsoft Windows, we should use WCF.

As their names imply, both HTTP GET and HTTP POST use HTTP as their underlying protocol. Both of these methods encode request parameters as name/value pairs in the HTTP request.

The GET method creates a query string and appends it to the script’s URL on the server that handles the request.

The POST method creates a name/value pairs that are passed in the body of the HTTP request message.

Asynchronous Call : Application can make a call to the Webservice and then continue todo watever oit wants to do. When the service is ready it will notify the application. Application can use BEGIN and END method to make asynchronous call to the webmethod. We can use either a WaitHandle or a Delegate object when making asynchronous call.
The WaitHandle class share resources between several objects. It provides several methods which will wait for the resources to become available
The easiest and most powerful way to to implement an asynchronous call is using a delegate object. A delegate object wraps up a callback function. The idea is to pass a method in the invocation of the web method. When the webmethod has finished it will call this callback function to process the result
Synchronous Call : Application has to wait until execution has completed.