When is a fragmented disk drive not fragmented? When you check it with Windows Disk Defragmenter. Strange as it may seem, Windows can report that a disk is not defragmented where other disk defragmenter tools report that that it is fragmented.
Running Disk Defragmenter is a bit strange in Windows 8 and from the Start screen just start typing defragment. Click Settings in the Search panel on the right and then click Defragment and optimise your drives on the left.
You can then select the drive and click Analyse. After a short analyses it will display the percentage of fragmented files. If there is any fragmentation then you can go ahead and defragment it.
Sometimes it reports that there is no fragmentation when there is. Perhaps it is just a rounding error and 0.9% is rounded down to zero. It is certainly possible to find fragmented files and one option is to use IObit SmartDefrag. This gives a better fragmentation report where you can see the number of fragments and also a choice of defragmentation options.
It is possible to find really fragmented files even though Windows says there aren't any. Fix them with SmartDefrag. I use the portable version from portableapps.com rather than the one direct from IObit. I try not to install software into Windows if I can help it, it avoids problems.