Microsoft became the first company to close a trading day above a $500 billion market capitalization in 1999.
Microsoft passed the $500 billion threshold during the technology-stock boom of 1999. Its valuation reflected the dominance of Windows on personal computers, the popularity of Microsoft Office, and investor expectations for continued growth in software and internet-related markets.
Founded in 1975 by Bill Gates and Paul Allen, Microsoft had grown from a programming-language supplier into a major software company. Its agreement to provide an operating system for IBM-compatible personal computers helped establish Windows as a central platform in the PC industry.
The 1999 milestone occurred before the dot-com bubble burst. Microsoft’s market value later fell during the early-2000s technology downturn, illustrating that market capitalization is a changing market estimate rather than a permanent measure of a company’s worth.