Recovery Partition
Some manufacturers create a recovery partition. This is usually drive letter D when they do create one. It will have the recovery software and an image to reimage the system if needed. This partition is not very big and it is not designed for the user to use.
The manufacturer should make the partition hidden or where you cannot access it other than to do the recovery. Users have a tendency to try to use that partition to store their files. There is a couple of problems with that. The partition is not very large so it fills up quick. Another problem is that it can cause the recovery image to get corrupted and you will not be able to use it.
If you have a Recovery Partition (usually Drive D), do not use that partition for anything. If you have saved files in that directory, you should move them to drive C or another location.