Note that there shouldn't be any technical reason for not "being able to defragment a solid state disk", in the sense that you could start a defragmenter program and run it against the disk.

But doing so doesn't have the effect it does on non-solid state disks, as moving the clusters together won't actually speed up the disk.

On the other hand, what you will do is perform lots of unnecessary writes on the disk, and this will shorten, albeit slightly, the life-span of the disk.

Additionally, many solid-state disks does optimizations to lessen this problem by reducing repeated writes to the same area, and this is transparent to the outside system, in which case the clusters might not be moved together at all but instead spread out over the disk. This technique is typically "wear leveling".

If a defragmenter program refuses to defragment a solid state disk (or even just list it as a disk you can select), I'd wager that it's basically a software refusal to do so, just to avoid the problems outlined above.

Note that I don't know enough about the underlying protocols used to defragment a disk, so there might very well be a hard block from a solid state disk to accept defragment commands, if there are such things. The reasons for this, however, are the ones described here.

Note that there shouldn't be any technical reason for not "being able to defragment a solid state drive", in the sense that you could start a defragmenter program and run it against the drive.

But doing so doesn't have the effect it does on non-solid state drives, as moving the clusters together won't actually speed up the drive.

On the other hand, what you will do is perform lots of unnecessary writes on the drive, and this will shorten, albeit slightly, the life-span of the drive.

Additionally, many solid-state drives does optimizations to lessen this problem by reducing repeated writes to the same area, and this is transparent to the outside system, in which case the clusters might not be moved together at all but instead spread out over the drive. This technique is typically "wear leveling".

If a defragmenter program refuses to defragment a solid state drive (or even just list it as a drive you can select), I'd wager that it's basically a software refusal to do so, just to avoid the problems outlined above.

Note that I don't know enough about the underlying protocols used to defragment a drive, so there might very well be a hard block from a solid state drive to accept defragment commands, if there are such things. The reasons for this, however, are the ones described here.