The computing giant's closing price on September 29 was $214bn (£137.4bn) while the Windows platform holder's was valued at $213.2bn (£136.8bn), BBC News reports.
IBM has enjoyed an extended period of steady growth, and Microsoft has suffered a decline. The move sees the former become the second most valuable technology firm in the world, behind Apple, who hold $362bn (£232bn) of the market.
According to Bloomberg figures, IBM's share price is now 22% higher than it was at the start of 2011. Microsoft's has fallen by 8.8%.
Analysts attribute the trend to IBM's decision to sell off its PC manufacturing business to Chinese firm Lenovo to focus on software and services.
"IBM went beyond technology," said Ted Schadler, a Forrester Research analyst. "They were early to recognise that computing was moving way beyond these boxes on our desks."
Microsoft also derives much of its revenue from software, such as its Windows operating system. The report notes that the company is currently between iterations of the OS. Windows 8 is slated for release in 2012.
Some industry experts have predicted that the rise of tablet devices and other portable media could spell the end of PC devices.
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