title: What exactly are the "components" of Rails (ActiveRecord, ActionController, etc.)?
body: <p>I just started learning Rails and Ruby. The Ruby on Rails Guide at <a href="http://guides.rubyonrails.org/getting_started.html" rel="nofollow">http://guides.rubyonrails.org/getting_started.html</a> says that Rails consists of many different "components". Some of these components, such as ActiveRecord and ActionController, I've encountered in my Rails apps (in models and controllers, respectively). </p>
  
  <p>The relevant syntax ("class Model &lt; ActiveRecord::Base" and "class ApplicationController &lt; ActionController::Base") make it look like these components are Ruby modules, but if they are modules in which files are they located? And how can we reference them without first using the Ruby method "require"?</p>
  
  <p><strong>UPDATE</strong>: So I found all of the built-in modules and classes. On my server, the path for the Base class of the ActiveRecord module (for example) is: </p>
  
  <pre><code>/usr/lib/ruby/gems/1.8/gems/activerecord-3.0.9/lib/active_record
  </code></pre>
  
  <p>But I still don't know why we can refer to these modules and classes in our models and controllers without first using Ruby's require method.</p>