There are following difference between both of them.
Hosting
Web Service: It can be hosted only on IIS (Internet Information Service).
WCF: It can be hosted in IIS (Internet Information Service), WAS (window activation service), Self Hosting and Window Service.
Attributes
Web Service: In Web Service, [WebService] and [WebMethod] attributes are used respectively with Class and Method.
WCF: In WCF, [ServiceContract] and [OperationContract] attributes are used respectively with Class and method which exposed to Client.
Protocols Support
Web Service: It supports only HTTP protocol for communication.
WCF: It supports HTTP, TCP, Named Pipes and MSMQ for communication.
Tools
Web Service: WSDL.exe tool is used to generate client for web service.
WCF: Service Metadata tool (svcutil.exe) is used to generate client for WCF service.
Operation
Web Service: In Web Service for communication with application, it used One-Way and Request-Response operation.
WCF: But wcf supports One-Way, Request-Response and one more operation Duplex operation.
Serialization
Web Service: It uses xml serialization using System.Xml.Serialization namespace.
WCF: It uses DataContract serialization on runtime using System.Runtime.Serialization namespace.
Bindings
Web Service: It supports only SOAP or XML based binding.
WCF: It supports number of different type of binding like basicHttpBinding, wsDualHttpBinding etc.
Conclusion:
Today we learned main difference between a web service and wcf.
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