Microsoft became the first publicly traded company to surpass a $500 billion market capitalization.
Microsoft passed the $500 billion mark during the technology-stock boom of the late 1990s. Its Windows operating system had become a dominant platform for personal computers, while Office software strengthened the company’s position in homes, schools, and workplaces.
The milestone illustrated how rapidly software companies could gain value as personal computing expanded. It also showed why market-cap records should be tied to a date and market condition: a valuation can be crossed during trading and then lost later as prices move.
Microsoft’s market value at the time was based on its listed equity, not on the total value of the software industry or the economic value of every computer using Windows. Later companies reached the same level in very different industries and eras.