<i>The second two are both on windows, which until windows 7 was unable to schedule hyperthreading correctly.</i><p>Hyperthreading doesn't require any special OS support. As the wikipedia page states:<p><pre><code>  This technology is transparent to operating systems and 
  programs. All that is required to take advantage of hyper- 
  threading is symmetric multiprocessing (SMP) support in
  the operating system, as the logical processors appear as
  standard separate processors.</code></pre>