title: What role does A20 line plays in Protected mode?
body: <p>I am going through the protected mode part of x86. I just learnt about GDT. Before, I have studied that to get into Protected mode( ie : Using all 32bit address line) A20 gate must be enabled.
   So, the code to enable A20 must be in 16bit right?
   Recently when I went through the wiki.osdev site, I found that the code to enable A20 is written in x86 assembly. X86 assembly produces 32bit opcodes that cannot be loaded in 16bit mode right?</p>
  
  <p>please explain if possible.
   Thank you.</p>