Way back in the dark ages--before cell phones, reality TV, or social networks--there was big iron. In those archaic times, computers were actually used for computing, as opposed to watching porn or idiotic video clips. The computing giants of the day included IBM, Digital Equipment, Unisys (the marriage of Sperry and Burroughs), Data General, and Wang Laboratories.
The transition to personal computing and networking changed all that. IBM and Unisys survived by refocusing on services. The others didn't fair so well. Markets change. Companies that change with them survive. Those that anticipate change do better still. Those that resist change or change too slowly go the way of the dinosaur.