Story highlights Google's stock market value topped that of long-time rival Microsoft

Caps a decade-long struggle between leaders of the PC and internet eras

Google's stock market value topped that of long-time rival Microsoft for the first time on Monday, capping a decade-long struggle for dominance between leaders of the PC and internet eras of computing.

In the first flush of optimism that followed its IPO, investors nearly drove Google's value beyond that of Microsoft in 2007. However, the stock later retreated as Wall Street grew worried that the company was pouring money into loss-making ventures such as the YouTube video site and Android mobile operating system in a vain attempt to head off a slowdown in search of advertising growth.

"There's finally a realisation on the part of investors that this is a not a one-trick pony," said Youssef Squali, internet analyst at Cantor Fitzgerald.

Instead, Google is set to top Facebook this year to also become the biggest online display advertising company, with global revenues likely to hit $6bn, according to Mark Mahaney, internet analyst at Citigroup. It has also grabbed an early lead in mobile display advertising, and accounts for more than half of the market.

The revival of confidence in Google has lifted its shares by more than 30 per cent in the past three months.

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The changing of the guard in market value terms also reflects stock market unease surrounding the release later this year of Microsoft's Windows 8 operating system, an event that Steve Ballmer, chief executive, has described as a "bet the company" product cycle.

After losing out to Apple in smartphones and tablets, Microsoft is counting on the latest Windows to stimulate a new generation of touch-screen, hybrid devices that will put PCs back on the map. However, most corporate buyers wait a year or more before upgrading and investors are cautious about Microsoft's chances of winning back consumers whose heads have been turned by Apple devices.

Based on closing prices, Google's shares ended the day to value the company at $249.1bn, nearly $2bn more than Microsoft. Among tech concerns, the rise left Google second only to Apple, whose soaring share price has lifted its market value to $628bn.

In another symbolic rebalancing of the technology landscape, IBM, whose first fortune in mainframe computing was eclipsed by the rise of Microsoft, also recently rebounded to overtake the PC software maker in terms of stock market value. It has since fallen back and was valued on Monday at $241bn.

Although Google has finally won a grudging vote of confidence on Wall Street, it has also attracted less welcome attention from regulators. Anti-trust agencies in Washington and Brussels have indicated that they are moving closer to completing investigations into the company, and decisions are likely by the end of this year -- more than a decade after similar cases against Microsoft came to a head.