title: about hardware drivers in protected mode
body: <p>Recently, I'm trying to write a simple OS. This is a big project.<br/>
  when I'm writing my code, I'm wondering how modern OS contact hardware under protected mode<br/>
  In real mode, we can just call the bios interrupt to accomplish this job.<br/>
  But I'm wondering how to accomplish this goal in protected mode.(Is it using in and out instruction??)<br/>
  I traced some of the linux source code, but still can't find the appropriate code.</p>
  
  <p>I know it is a basic question to many people, plz help me, tks.<br>
  and sorry about my poor English. </p>