History of magnetic disk storage based on perpendicular magnetic recording

It is interesting to speculate about those shifts in technology, which could have been adopted earlier than they were. What would the consequences on subsequent technological advances have been? In magnetic disk storage, the change from longitudinal to perpendicular recording came close to occurring in the mid-fifties. This paper details the little-known circumstances surrounding decisions made by IBM's research and development group at 99 Notre Dame, San Jose, which had wide-ranging consequences in the development of magnetic disk drives.