The dominance of Windows has been Microsoft's greatest strength for decades, but the operating system is facing increased competition on all fronts.
Microsoft's long running battle with Linux is eroding its market share on the server side, while Apple is making slow but steady progress in the desktop and laptop businesses.
The situation is even worse on the mobile front, since Microsoft has never enjoyed the kind of dominance it has with PCs and servers in this market.
Apple, Google and RIM are all cutting into the market, and the response of analysts and customers to Microsoft's Windows Phone 7 mobile operating system has been tepid at best.
Microsoft is widely expected to release Windows 8 some time in 2012, and regular refreshes are expected every two to three years after that, but is the operating system in long-term decline?
"A decline would seem to be logical, but Windows is not expected to enter into a decline, although the dynamics of the question have changed," Al Gillen, programme vice president of system software at IDC, told V3.co.uk.
"Today we've got an explosion in other types of devices besides the PC that people use. But, at least in the developed world, these tend to augment rather than replace the standard PC."
Gillen argued that there is still a healthy demand for PCs running Windows, much as there is for established technologies like televisions, because the replacement market is still there.
Figures from Intel suggest that around one million PCs are sold worldwide every day, the vast majority running Windows. This is unlikely to change any time soon, but emerging markets may alter this, according to Charles King, principal analyst at Pund-IT.
"No knock on Apple for its success, but its sales numbers look puny by comparison," he told V3.co.uk.
"A serious problem I see for Microsoft is that the emerging/growth markets that it has been cultivating for so long are where some of the most innovative uses of mobile technologies are occurring.
"The bottom line is that, by the time those consumers are 'ready' for PCs, their attentions may have shifted elsewhere."
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