apache, nginx, IIS are web servers mongrel, webrick, phusion passenger are app servers

App server is something which works with particular programming language and PARSES and executes the code

since mongrel and webrick can only work with rails, so they are app servers

Web servers are servers which can take the request from the BROWSER.

Web servers normally works on port 80 THOUGH we can change the port in configuration

since mongrel and webrick can take that request directly, so they can be thought of as web servers but web servers do have a lot of other functionality like request pipeline, load balancing etc.

App servers LACK these functionalities.

apache, nginx, IIS are web servers mongrel, webrick, phusion passenger are app servers

App server is something which works with particular programming language and parses and executes the code

since mongrel and webrick can only work with rails, so they are app servers

Web servers are servers which can take the request from the browser.

Web servers normally works on port 80 though we can change the port in configuration

since mongrel and webrick can take that request directly, so they can be thought of as web servers but web servers do have a lot of other functionality like request pipeline, load balancing etc.

App servers lack these functionalities.