title: What's the difference between "C system calls" and "C library routines"?
body: <p>There are multiple sections in the manpages. Two of them are:</p>
  
  <pre>
  2     Unix and C system calls
  3     C Library routines for C programs
  </pre>
  
  <p>For example there is <a href="http://developer.apple.com/documentation/Darwin/Reference/ManPages/man3/getmntinfo.3.html" rel="noreferrer"><code>getmntinfo(3)</code></a> and <a href="http://developer.apple.com/documentation/Darwin/Reference/ManPages/man2/getfsstat.2.html" rel="noreferrer"><code>getfsstat(2)</code></a>, both look like they do the same thing. When should one use which and what is the difference?</p>