title: Correct interrupt code in assembly
body: <p>I want to print sum of two numbers in assembly. When I run the code, compiler shows the message:</p>
  
  <blockquote>
    <p>INT 21h, AH=020h  - not supported yet. refer to the list of supported
    interrupts.</p>
  </blockquote>
  
  <p>Why do my code produce this error? What Interrupt code should I use?</p>
  
  <pre><code>.MODEL SMALL
  .STACK 100H
  .DATA
  A DW 5H
  B DW 2H
  SUM DW ?
  .CODE
  MAIN PROC
  MOV AX,@DATA
  MOV AX,A
  ADD AX,B
  MOV SUM,AX
  INT 21H
  
  MAIN ENDP
  END MAIN
  </code></pre>