title: In MIPS, what's the difference between signed addition, unsigned addition, signed subtraction and unsigned subtraction?
body: <pre><code>add rd, rs, rt
  addu rd, rs, rt
  sub rd, rs, rt
  subu rd, rs, rt
  </code></pre>
  
  <p>In MIPS, what's the difference between signed addition, unsigned addition, signed subtraction and unsigned subtraction? If their results are the same, what's the point to classified as using signed and unsigned methods?</p>