Related to 2), the answer is hierarchies. Related to 1), the linked article writes: (For those who want to nitpick, I know Dropbox is not fully centralized; it

Related to 2), the answer is hierarchies. Related to 1), the linked article writes: (For those who want to nitpick, I know Dropbox is not fully centralized; it uses AWS S3 for storage and Dropbox-company servers for metadata management. Also, it employs data parallelism in the backend for scalability, but, on the spectrum, it is closer to a centralized architecture than a fully decentralized one.) The point is to compare a more centralized architecture to a more/fully decentralized architecture.