8 GB missing in partition

It seems like I am unable to fully utilize a drive on my Windows laptop. My D:\ drive is shown (in "This PC") as being 68.4/175 GB filled which means that 106.6 GB is used. But I can see that only 98.2 GB is used if I select all the folders (including hidden) at the top level of the partition and check the size on disk. So there is 8.4 GB unaccounted for. My recycle bin has less than 9 MB, so that is not the issue here. Is this because I have compressed that drive? Could someone please help me with this?