Why does defragging only INcrease the amount of immovable data?

Factual Questions
1

Earlier today, I decided to optimize my hard drive after moving a lot of data around. About 7% of the disk was still fragmented, though, so for the heck of it I ran Norton Speeddisk again. When it was done, I noticed that there was still about the same level of fragmentation, but there was for some reason more immovable data than the first time around. What’s more, some of the immovable clusters had… Moved.

Here’s what it looked like the first time around today:

And here’s what it looked like the second time around:

:confused: ?

Can anybody explain this?

2

Immovable clusters are simply pieces of data that are in use at the time that you run defrag. At different times, different pieces and amounts of data will be in use.