The tumble has shaved roughly $230 billion off Apple’s market value, placing it close to losing its position as the most valuable publicly traded company to Microsoft.

The two companies have competed since the mid-1970s, when both were founded. Microsoft dominated its rival in the 1990s, riding the popularity of its Windows operating system to become the largest publicly traded company by the end of the decade. During that time, Apple flirted with going broke.

But that dynamic reversed. Microsoft’s shares and its market value stagnated for more than a decade after the dot-com bust. Powered by the release of products like the iPod and later the iPhone, Apple’s shares marched higher.

By 2010, Apple’s market value had passed Microsoft’s, and the gap between the two continued to grow, reaching as much as $400 billion in 2015. As recently as a month ago, Apple was worth around $250 billion more than Microsoft.

In recent weeks, investors have grown increasingly concerned about iPhone sales. A number of Apple suppliers cut their financial outlooks for this quarter, suggesting there may be weaker demand for the latest models of the phone than expected. Last quarter, sales of iPhones accounted for nearly 60 percent of Apple’s revenue.