Generic handler:As per MSDN Generic Handler is a default handler which will have @webhandler directive and has .ashx extension this generic handler is not having UI but it provides response when ever any request made to this handler.
HTTP Handler:HTTP Handler is a process which runs and continue to server request and give response based on the request handling code. This handler does not have UI and need to configured in the web.config against extensions. One of the great example of Http Handler is page handler of ASP.NET which serves .aspx pages request.
Difference between generic handler and http handler:Following is a main differences between http handler and generic handler.
- Generic handler has a handler which can be accessed by url with .ashx extension while http handler is required to be configured in web.config against extension in web.config.It does not have any extension
- Typical example of generic handler are creating thumbnails of images and for http handler page handler which serves .aspx extension request and give response.