|By your own numbers that is not be the reason for the low disk space notification. If there were a Vista partition the shown partition would be smaller than 111GB. |
Without explaining why your total space of 111GB is roughly what a 120GB formatted drive should show.
Most likely reasons for the discrepancy is your recycle bin. Could also be slack space, if the drive is formatted using FAT32. FAT32 would waste a large amount of storage space. The reason for that is that every file on your computer must occupy a cluster. Using FAT32 on a 120GB drive results in 32kb clusters.
That means a file of ONLY 1kb will use 32kb of space. This is called slack space and accounts for the differences in the numbers.
The actual total file size on the drive is different than the occupied space. This occurs to a lesser degree even with NTFS. However, the default cluster size for NTFS is 4kb.
There are other causes for the numbers you see but for now go to disk management and see how the partition is formatted. And empty the recycle bin.