My favorite ones would show you a grid representing all the clusters on the disk.  You would see an open block for free space and a solid block for allocated space.<p>Then it would highlight a span of blocks to indicate reading.<p>Finally it would write those clusters elsewhere, indicating so with a different color.<p><i>Edit:</i> Uhh..  and HN deleted my diagrams.  See <a href="http:&#x2F;&#x2F;pastebin.com&#x2F;raw.php?i=nKHddiKe" rel="nofollow">http:&#x2F;&#x2F;pastebin.com&#x2F;raw.php?i=nKHddiKe</a>