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.

Then it would highlight a span of blocks to indicate reading.

Finally it would write those clusters elsewhere, indicating so with a different color.

Edit: Uhh.. and HN deleted my diagrams. See http://pastebin.com/raw.php?i=nKHddiKe

For your enjoyment: https://www.youtube.com/watch?v=kPv1gQ5Rs8A

Neat. I had one for DOS too that would go left-to-right instead of top-to-bottom, but I don't remember if it was a Norton tool or something else. It was mesmerizing to me as a kid to watch data moving around on the hard drive and the computer magically getting faster.

Norton Speed Disk? http://virtuallyfun.superglobalmegacorp.com/wordpress/wp-con...

The Windows 95 Defragmenter was probably based on this, since it has a Symantec copyright alongside Microsoft's.

Agreed, very soothing and hypnotic to watch!