title: understanding sync and asyn operations
body: <p>I am learning how to make sync and asyn operations . Please correct me what i have mentioned/learned are right:</p>
  
  <ol>
  <li><p>sync and asyn operations can be done in following ways(we can pick any according to our requirement)</p>
  
  <ul>
  <li>GCD</li>
  <li>NSThread</li>
  <li>NSOperationQueue-adding NSOperation </li>
  </ul></li>
  </ol>
  
  <p>2 . GCD is an C API and on top of it  - NSThread and NSOperationQueue,NSOperation are written</p>
  
  <p>3 . NSOperation is nothing but a Thread which has number of tasks within it . Same like main() is Thread . If someone written creating thread which also means creating custom nsoperation</p>
  
  <p>4 . NSConnectionurl,AFNetwork are on top of these GCD,NSThread,NSOperationQueue,NSOperation</p>