America’s biggest technology companies are combining Silicon Valley returns with Ruhr Valley balance-sheets. Investors who bought shares in Alphabet, Meta and Microsoft a decade ago are sitting on eight times their money, excluding dividends. Spending on data centres means the firms possess property and equipment (accounting-speak for hard assets) worth more than 60% of their equity book value, up from 20% over the same period. Add the capital expenditure of these firms during the past year to that of Amazon and Oracle, two more tech giants, and the sum is greater than the outlay of all America’s listed industrial companies combined. Jason Thomas of Carlyle, an investment firm, estimates that the spending boom was responsible for a third of America’s economic growth during the most recent quarter.