When I am interviewing .NET developers I often ask this question: what is the difference between a Web Service and a WCF service. Many people don't know the exact difference between them, that's why I decided to write a blog about this topic.

Here are the few differences.

• Web services can be hosted in IIS as well as outside of the IIS. While WCF service can be hosted in IIS, Windows activation service,Self Hosting,WAS and on lots of protocols like Named Pipe,TCP and others.Many people disagree how we can host the web service outside of the IIS but Here is the article for that.http://msdn.microsoft.com/en-us/library/aa529311.aspx.
• In Web Services Web Service attribute will added  on the top of class. In WCF there will be a Service Contract attributes will be there. Same way Web Method attribute are added in top of method of Web service while in WCF Service Operation Contract will added on the top method.
• In Web service System.XML.Serialization is supported while in the WCF Service System.RunTime.Serialization is supported.
• WCF Services can be multithreaded via ServiceBehavior class while web service can not be.
• WCF Services supports different type of bindings like BasicHttpBinding, WSHttpBinding, WSDualHttpBinding etc.while Web services only used soap or xml for this.
• Web services are compiled into a class library assembly. A file called the service file is provided that has the extension .asmx and contains an @ WebService directive that identifies the class that contains the code for the service and the assembly in which it is located while in WCF.WCF services can readily be hosted within IIS 5.1 or 6.0, the Windows Process Activation Service (WAS) that is provided as part of IIS 7.0, and within any .NET application. To host a service in IIS 5.1 or 6.0, the service must use HTTP as the communications transport protocol.

Hope this will help you. Happy programming!!!