In what ways do the database architecture change when one discards the assumption that I/O is the bottleneck? Does it obviate the relational model? I always fou

In what ways do the database architecture change when one discards the assumption that I/O is the bottleneck? Does it obviate the relational model? I always found the relational model to fit working with data sets very well since it's nice and declarative. Does that turn out to be a bottlneck assuming fast I/O?