Definition of "System Backup"

I am running a Win 7/64 machine with 2 (physical) hard drives, each of which are partitioned; Disk 0 contains the O/S and all software except games in C:/, and sector reserved for the swap file in Z:/.

Disk 1 is partitioned into D:/ (clipart for websites), E:/ (Games) and F:/ (data, word & excel files, pictures, music, videos, downloads and generally all the files I created)

I also have 3 external USB hard drives.

The question is as follows; under the “Home” tab of Comodo Backup, what does the “System Backup” button backup? After performing this task and purely based on size I doubt that it has backed up all of my drives and partitions, does this mean that I need to then backup each drive individually? What is the difference between “system backup” and just backing up all of drive 0?

Thanks in advance.