title: Difference between the `event loop phases` such as `I/O callback` and `poll`
body: <p>I am unable to understand the difference between the two phases <code>I/O callback</code> and <code>poll</code> while reading through the mechanism of <code>event loop</code> of Node.js. </p>
  
  <p>My understanding is as follows. Please correct if it's wrong: <br><br>
  For example, When we try to read the file asynchronously, the <code>poll</code> phase receives the I/O instruction to read the file (so, the reading the file happens in poll phase?) and adds the <code>callback</code> of <code>fs.readFile()</code> to the <code>I/O callback</code> phase (callback of <code>fs.readFile</code> executes in <code>I/O callback</code> phase?). </p>