When his computer failed, he found out his backup was not working. It was just going through the motions. Disks are cheap and can hold 650 megabytes of data. Disks are compatible with the CD-ROM drives. Some blank CDs may be incompatible with some CD writers.
Disks are expensive.
Disks can hold 100 or 250 megabytes, depending on model. As easy to use as a floppy drive. Disks are more expensive than blank CDs. Compatibility with other computers can be a concern because not everyone has a Zip drive. SuperDisks can hold up to 120 megabytes.