Which technology has affected tape storage capacity the most?

The biggest development in tape storage capacity was probably a demonstration by Fujifilm and IBM of Barium Ferrite perpendicular magnetic recording. It's basically using a new surface coating and manufacturing process on tape that gives us an uncompressed capacity of 154 TB per tape cartridge on a single LTO cartridge.

These cartridges don't cost a lot of money, so we're probably talking about the lowest cost per gigabyte that's ever been invented for storage. Barium Ferrite has been the story for a few years now when it comes to increased tape storage capacity. Historically, tapes have been coated with magnetic particle technology.

Perpendicular magnetic recording on disc allows us to squeeze a lot more data on to the same amount of turf. It is accomplished by running a small static electric charge through it during manufacturing. Barium Ferrite does that through a chemical process on the tape media. In the past, this was believed to be impossible because tape is flexible and doesn't have a rigid surface.

Sony also demonstrated a different methodology for coating tape that it says will get you to 180 TB per cartridge uncompressed. But that hasn't been prioritized yet. I would say Fujifilm is a better bet. They actually have the processes in place to deliver.