title: hexadecimal value of opcodes
body: <p>I created a very simple assembly program that prints the letter 'a' in DOS. 
  I opened it in a hex editor and the result was this: </p>
  
  <p>Assembly code: </p>
  
  <pre><code>mov ah, 2 
  mov dx, 'a' 
  int 21h 
  </code></pre>
  
  <p>Hex code </p>
  
  <pre><code>B4 02 B2 61 CD 21
  </code></pre>
  
  <p>I wanted to understand how it was generated! Like, I do not know if I'm right, but I realized that: </p>
  
  <pre><code>B4 = mov ah 
  02 = 2 
  B2 = mov dx 
  61 = 'a' 
  CD = int 
  21h = 21
  </code></pre>
  
  <p>The <code>02</code>, <code>61</code> and <code>21</code> I understood what turned but and <code>B4</code>, <code>B2</code> and <code>CD</code>?</p>