When you perform a backup using Schedule Folders, only the data, along with the folder tree, is compressed and stored.
Backing up disks and partitions is performed in a different way: Schedule Volumes stores a sector-by-sector snapshot of the disk, which includes the operating system, registry, drivers, software applications and data files, as well as system areas hidden from the user. This procedure is called creating a disk image, and the resulting backup archive is often called a disk/partition image.
Only those hard disk parts that contain data are stored. Further, it does not back up swap file information. This reduces image size and speeds up image creation and restoration.