title: The real meaning of $ and $$ in a sample code in NASM
body: <p>I saw a code like below:</p>
  
  <pre><code>section .data
     db 'hello'
     db  'h', 'e', 'l','l','o'
     data_segment_size  equ $-$$
  </code></pre>
  
  <p>Why <code>data_segment_size</code> is equal to 25? I know what $ and $$ indicate, but I can't figure out why this variable is 25 according to my book. maybe that is a mistake in that book.</p>