What is the cheapest archival media?

Hard disks might seem cheaper at first due to their lowest price per byte. In reality, optical discs are cheaper in the long term due to their reliable and failproof design.

 

Optical discs are immune against unannounced failures such as head crashes and malfunctioning memory controllers by design, in addition to being water resistant and the write-once variants being non-overwriteable, which provides protection against software bugs and malware.

 

Hard disks indeed are cheaper in the short term, but this is defeated in the long term due to their shorter and uncertain lifespan, thus higher redundancy requirements.

 

In addition, only optical media is immune against electromagnetic impulses and water, therefore the likeliest media to survive natural disasters.