title: what's the different between -mtune=i486 and -arch=i486
body: <p>I have an old code need compiled with <code>-m486</code> flag in <code>GCC</code>. 
  But there is no that flag. Then I found <code>-mtune=i486</code> and <code>-arch=i486</code><br>
  I have read this <a href="http://gcc.gnu.org/onlinedocs/gcc-4.7.2/gcc/i386-and-x86_002d64-Options.html#i386-and-x86_002d64-Options" rel="noreferrer">page</a>.
  But still don't know which is the best one for <code>-m486</code>?</p>