Recently, Nvidia $NVDA (brown) surpassed $4 trillion in market capitalization and also accounted for over 8% of the S&P 500. The last time a stock was over 8% of the $SPX was 56 years ago, IBM (green) in 1969. Interesting historical facts: Also in 1969, the Justice Department filed an antitrust suit against IBM, accusing it of being a monopoly (it was dropped in 1982). The only other stock to exceed 8%, AT&T, was also accused by the Justice Department of being a monopoly in 1949. This case was successful, and it was broken up in 1984.