I don't know if it's fair to say that ext4 "started" in 2006, given that it was an evolution of ext3, which was an evolution of ext2 (which I assume was an evol

I don't know if it's fair to say that ext4 "started" in 2006, given that it was an evolution of ext3, which was an evolution of ext2 (which I assume was an evolution of ext?), to the point that you can still mount an ext2 filesystem as a very feature-limited ext4 filesystem.