  terminology: upcall vs callback? 
 The Question is:
 
What is the difference between a "callback"
and an "upcall" ?
 
Thanks,
Raj Mohan
 
 
 The Answer is:
 
  The context -- in DECthreads, an upcall is a callback used by OpenVMS
  to inform DECthreads that something "interesting" has happened.  In the
  more traditional OpenVMS context, callbacks are typically used to refer
  to user-written calls registered by users for certain events.
 
 
