Largest computer

The largest computer ever built was the SAGE (Semi-Automatic Ground Environment) system – 56 IBM AN/FSQ-7 computers spread over 20,000 ft². The computer was built by IBM with MIT and RAND providing systems design and software respectively. Construction began in the 1950s and was completed in 1963. The SAGE system was also the most expensive computer ever built, at an estimated cost of $4–12 billion. It stayed operational for more than 20 years.

According to the IBM: When fully deployed in 1963, SAGE included 23 centers, each with its own AN/FSQ-7 system, which really consisted of two machines (one for backup), both operating in coordination. Ultimately, 54 systems were installed, all collaborating with each other. The SAGE system remained in service until January 1984, when it was replaced with a next-generation air defense network.