A disk or volume backup stores a disk or a volume file system as a whole, along with all the information necessary for the operating system to boot. It is possible to recover disks or volumes as a whole from such backup, as well as individual folders or files.
With the sector-by-sector (raw mode) option enabled, a disk backup stores all the disk sectors.
For supported file systems, with the sector-by-sector option turned off, a disk or volume backup stores only those sectors that contain data. This reduces the resulting backup size and speeds up the backup and recovery operations.
Windows
The swap file (pagefile.sys) and the file that keeps the RAM content when the machine goes into hibernation (hiberfil.sys) are not backed up. After recovery, the files will be re-created in the appropriate place with the zero size.
A volume backup stores all other files and folders of the selected volume independent of their attributes (including hidden and system files), the boot record, the file allocation table (FAT) if it exists, the root and the zero track of the hard disk with the master boot record (MBR). The boot code of GPT volumes is not backed up.
A disk backup stores all volumes of the selected disk (including hidden volumes such as the vendor's maintenance partitions) and the zero track with the master boot record.
Linux
A volume backup stores all files and folders of the selected volume independent of their attributes; a boot record and the file system super block.
A disk backup stores all disk volumes as well as the zero track with the master boot record.