title: Why do B* instances have a significantly slower start time than F* instances on Google App Engine?
body: <p>I was recently reading <a href="https://medium.com/google-cloud/understanding-and-profiling-app-engine-cold-boot-time-908431aa971d" rel="nofollow noreferrer">Understanding and Profiling App Engine Cold-Boot Time</a> which discusses various items relating to cold-boot time of Google App Engine instances (i.e. the time it takes to start up an instance). While discussing the cold-boot time of an F2 instance, the author writes:</p>
  
  <blockquote>
    <p>(Note, if you’re wondering why the B1,B2,B4 instances have significantly slower time, we will talk about that in a future post)</p>
  </blockquote>
  
  <p>Unfortunately, I have not been able to find this "future post" that the author references, and have not been successful at finding this idea mentioned in any of the Google App Engine documentation online.</p>
  
  <p>As quick background, the F1, F2, etc. instances are the names of different classes of frontend instances on Google App Engine, while the B1, B2, etc. are the names of difference classes of backend instances. (<a href="https://cloud.google.com/appengine/docs/standard" rel="nofollow noreferrer">more information can be found in Google's documentation here</a>)</p>
  
  <p>So my questions are:</p>
  
  <ul>
  <li>Is this still true?</li>
  <li>And if so, what is the cause of this discrepancy in cold-boot time?</li>
  </ul>