zf2 ServiceManager vs ServiceLocator

zf2 ServiceManager vs ServiceLocator

I am learning zf2, reading docs, tutorials etc from the web. Now I am
confused regarding Zend\ServiceManager\ServiceManagerAwareInterface.php
and Zend\ServiceManager\ServiceLocatorAwareInterface.php.
Also in some place (like controller) I use $this->getServiceLocator() to
fetch the ServiceManager object while at some other places we use
->getServiceManager() and it also returns the same ServiceManager object.