Hi
The options are an External Drive, a Separate Internal Drive, (not a partition, if the drive fails you will lose both) or DVDS.
If you have a small enough C:\ drive then you could do it to disks and make the backup self bootable. I have a backup like this for my original setup before software was installed, on a Flash Drive (another option).
Just put in disk number one and install the backup.
For most people this isn't a real option because it would take a whole stack of disks.
I have my backup on a second hard drive in my computer, but the best bet is to create it on an external drive that you only turn on when you are using it. The drive will get little use, be protected from malware, and the backup will not depend on your internal drives.
I recently got hit by lightning, all of my data (everything) was backed up on several external drives and I didn't lose anything.
It could have been a disaster, I don't use a backup program to backup my data, I copy the files uncompressed to my backup drive.
I don't want to take the risk of having a corrupted backup file that won't open.
I've had that happen in the past.
I Now have one master plug I can pull, and I unplug everything during thunderstorms.
Mike