title: Why can't horizontal span be implemented on Vista?
body: <p>Until Windows Vista, ATI and nVidia supported a feature called horizontal span, which combined two monitors into a single larger screen.</p>
  
  <p>This feature allows the taskbar to span across both monitors, allows games to be played in fullscreen across both monitors, and allow Remote Desktop Connection to span both monitors without the <code>/span</code> feature (I have four monitors, so my total screen width is more than RDP's limit of 4096 pixels, making <code>/span</code> very annoying.  Also, the ActiveX control doesn't support it)</p>
  
  <p>The Vista drivers from these companies do not support this feature, and it appears that they never will.</p>
  
  <p>What changes were introduced by the <a href="http://en.wikipedia.org/wiki/Windows_Display_Driver_Model" rel="nofollow noreferrer">WDDM</a> that made this feature impossible?</p>