Digital Equipment Corporation (DEC) was the most successful minicomputer firm in history. At its high point, it had multiple large campuses and amazing facilities, and even ran helicopters between them and to Logan Airport in Boston where they had their own gate. (I rode them. Very cool.) Their PDP and VAX series computers were crucial to the development of ARPANET and its evolution into the Internet.
It seemed impossible for DEC to vanish. But due to a series of market changes and poor decisions by management, they are now only a memory. Their productive period was about 30 years, from 1960 to 1990. This 30 year period is a not uncommon one for corporate arcs.
#Google is now 25 years old.