Big tech companies are rebuilding computer systems from the bottom up to accommodate artificial intelligence (A.I.), reshaping technology, finance, energy, and communities. The shift in computing is driven by specialized computer chips called graphics processing units (GPUs) that can run math faster and analyze more data than traditional chips. Tech companies are constructing data centers packed with GPUs, which require more electricity and cooling. The demand for power is straining local utilities, leading companies to turn to nuclear power and other solutions. The A.I. boom is accelerating the need for more computing power and changing the way data centers operate.