Wikipedia
Multivac is the name of a fictional supercomputer in many stories by Isaac Asimov. According to his autobiography In Memory Yet Green, Asimov coined the name in imitation of UNIVAC, an early mainframe computer. Asimov had assumed the name "Univac" denoted a computer with a single vacuum tube (it actually is an acronym for "Universal Automatic Computer"), and on the basis that a computer with many such tubes would be more powerful, called his fictional computer "Multivac". His later short story " The Last Question", however, expands the AC suffix to be "automatic computer".
Like most of the technologies Asimov describes in his fiction, Multivac's exact specifications vary among appearances. In all cases, it is a government-run computer that answers questions, and is usually buried deep underground for security purposes. However, Asimov never settles on a particular size for the computer (except for mentioning it is very large) or the supporting facilities around it. " Franchise" states it is half a mile long and three stories high, at least as far as the general public knows, while " All the Troubles of the World" states it fills all of Washington D.C.. There are frequent mentions of corridors and people inside Multivac. Unlike the artificial intelligences portrayed in his Robot series, Multivac's interface is mechanized and impersonal, consisting of complex command consoles few humans can operate (with the exception of " Key Item"). Though the technology depended on bulky vacuum tubes, the concept – that all information could be contained on computer(s) and accessed from a domestic terminal – constitutes an early reference to the possibility of the Internet (see " Anniversary" for how it was used). In The Last Question, Multivac is shown as having a life of many thousands of years, growing ever more enormous with each section of the story, which can explain its different reported sizes as occurring further down the internal timeline of the overarching story.