Floppy: Good for incremental backups on a daily basis and perhaps the best solution for saving work as it progresses, but useless for system-wide restoration. The LS120 Disk and the Zip disk are not large enough or common enough to be considered for the sort of simple but complete backup considered here.
Hard Drive: One can back up to a separate partition on the same drive, which is of little use if that drive fails, or one can back up to another hard drive in the same computer. This is good, except there is a fair chance that a power supply failure or nearby lightning strike could fry both drives–or somebody could steal the computer–leaving nothing to restore.
Network Filesystem Transfer: This is a good solution to back up and restore files for someone interested enough to correctly install it. however, it does nothing for the process of getting the system up again to the point where one can restore the files. In short, it’s too complicated for most people to institute.
CD-ROM: This is where things begin to look interesting. These days most Linux users have a CD burner, and the availability of cheap CD-RW disks means the cost of maintaining something akin to the traditional rotating backup system is definitely manageable. This is the one for us.