Why do big gaps remain after defragmentation in Windows XP?

Question

I had the understanding that disk defragmentation in Windows XP reorganises your data so that files are contiguous along your hard drive. Every time I defragment my hard drive, I end up with blue coded contiguous files, but huge white gaps remain between the blue blocks.

Wouldn't this unnecessarily increase hard drive seek time and reduce disk performance? (since the read head has to move across that huge empty space to reach another file)

Thanks!

Oh and here is a screenshot showing the big white gap:

P.S. Is this because the stock Windows XP defragmenter is not very good, and there are better software out there? If so, what are some examples?

Solution

The point of defragmentation is – as the name suggests – avoiding the fragmentation of files.

Grouping free space is called compactation and may or may not be performed by a defragmentation utility. Windows XP's Disk Defragmenter doesn't. (source)

One free alternative with a few more options than the built-in utility is Defraggler.

For example, it allows you to Defrag Freespace, which is essentially compactation.

More utilities are also suggested in this SU question: Looking for an alternative to the Windows defrag utility

Comments

[Ƭᴇcʜιᴇ007]

It has to have enough room to move contiguous blocks around. So say you have 50% full (contiguous), and then you have a gap and then another contiguous block of 30% (in the remaining 50% space). There's not enough free space space (20% left) for it to copy the 30% block, before deleting the original copy of it. Does that sound like what you're running into? Perhaps post a screen-shot of what Defrag is showing you.

[Rob]

It also has issues moving system files and files being run by system processes. There are defrag tools that will run on boot and can take care of that.

[hpy]

Thanks for the answer and comments, they are very informative. :)