title: System threads vs not-system threads
body: <p>I noted that very often it occurs expression: "system thread". What does it mean in the fact? In particular, I cannot imagine <strong>not</strong>-system threads. Just, the system must be aware of thread. The operating system ( a scheduler) switches a context so he must know it!</p>
  
  <p>For example, on the fourth page it is written about system threads:
  <a href="http://www.dabeaz.com/python/GIL.pdf" rel="nofollow noreferrer">http://www.dabeaz.com/python/GIL.pdf</a></p>