Most expensive computer

The most expensive computer ever built was the SAGE (Semi-Automatic Ground Environment) system – it was also the largest (56 IBM AN/FSQ-7 computers over 20,000 square feet) and heaviest system (250 tons) ever built. Built by IBM with MIT and RAND providing systems design and software respectively, construction began in the 1950s, completed in 1963 at an estimated cost of $4-12 billion – in 1964 dollars; most estimates place the price at $8 billion. It stayed operational for more than 20 years.