Why default page is calling even though index.html.erb file in public folder is missing?

I am developing a simple ruby on rails app.The server has started successfully.Then when we go to the default web url localhost:3000/ the default route is called showing the home page about the instructions.But we dont want this so need to remove the index.html.erb file in the public folder under the main project directory.The real problem is the file is missing and still the default page is loading.

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What is really happening here and where is the index.html.erb file located.[Dont Mark it Duplicate because here the problem is different].How to call another route to show some mypage.html

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Server Log

Started GET "/" for ::1 at 2016-04-19 23:29:26 +0530
Processing by Rails::WelcomeController#index as HTML
  Rendered C:/RailsInstaller/Ruby2.2.0/lib/ruby/gems/2.2.0/gems/railties-4.2.5.1/lib/rails/templates/rails/welcome/index.html.erb (0.0ms)
Completed 200 OK in 36ms (Views: 35.1ms | ActiveRecord: 0.0ms)

Files in public folder:

400.html
422.html
500.html
favicon.ico
robots.txt