Applications running in a Docker container see a single filesystem which they can read from and write to in the usual way for the operating system. The container sees a single filesystem drive but it's actually a virtual filesystem, and the underlying data can be in many different physical locations.

Files which a container can access on its C drive could actually be stored in an image layer, in the container's own storage layer, or in a volume that is mapped to a location on the host. Docker merges all of these locations into a single virtual filesystem.