Next year, on April 4^th 2010, Microsoft will celebrate its 35^th birthday. For comfortably more than a quarter of a century the company has dominated desktop computing.

Today, with offices in more than 100 countries, assets in excess of $70 billion and almost 90,000 employees, Microsoft finds its supremacy threatened on several fronts.

Coming late to the internet because, as Bill Gates admitted, when it came along, “we had it as a fifth or sixth priority,” Microsoft has been unsuccessfully forced to play catch-up ever since.

Despite its Internet Explorer browser enjoying a market share of nearly 70%, the company has humiliatingly failed to prevent Google from becoming the dominant operator in the online universe.

Similarly, as mobile phones have morphed in to miniature computers, all attempts by Microsoft to successfully establish Windows Mobile as the smartphone operating system of choice have so far largely failed.

According to researcher IDC, in the United States the BlackBerry operating system from RIM currently enjoys more than 48% of the total smartphone market, with the Mac OSX, deployed only on the iPhone, in second place with 19%. Windows Mobile comes third with 15%.

Of the handset manufacturers still choosing to install Windows Mobile only HTC, thanks to their TouchFlo interface, have succeeded in offering a finger friendly touchscreen implementation. Others, like Motorola and Palm, have begun to look elsewhere.

Of course, 15% market share is not to be unthinkingly dismissed. Apple, for example, would be delighted were OSX to be deployed on that proportion of PCs. But with Windows installed on nearly 90% of all personal computers, and with some commentators starting to suggest that smartphones could yet replace many PCs, Microsoft’s position could become precarious.

Making matters worse IDC predict that over the next five years the share of the smartphone market enjoyed by Google’s Android operating system could rise from 7.5% to 15%, while thanks to the Pre, Palm could see their share grow from nowhere to 8%.

That growth will have to come from somewhere and, as things stand, much could be at Microsoft’s expense.

Under attack on several fronts, the Redmond monolith is attempting to fight back.

In an almost certainly doomed challenge to Google in the obscenely lucrative market for internet search, Microsoft recently rebranded their offering as Bing. Unfortunately, although the improved engine produces comparable results to Google, and even boasts some nice presentational touches, it fails to provide users with any compelling reason to switch allegiance. A month after the heavily promoted relaunch, researcher StatCounter estimates that Microsoft’s share of search only rose from 7.8% to 8.23%.

Were that not bad enough Google have just announced Google Chrome OS will appear in the second half of next year. Initially targeting netbook users, Google is about to come in to conflict with Microsoft in the one area where Windows has been historically pre-eminent, namely PC operating systems.

According to Sundar Pichai, vice president of product management at Google, the Chrome OS is "our attempt to re-think what operating systems should be". Allegedly speed, simplicity and security are the key aspects and, in what can only have been a direct reference to Internet Explorer, he added: “We are completely redesigning the underlying security architecture of the OS so that users don't have to deal with viruses, malware and security updates.”

Significantly, unlike Windows, the new OS is to be based on open-source Linux code, which allows third-party developers to design compatible applications. And again, although this has yet to be confirmed, unlike Windows but like so many other Google offerings, the Chrome OS may be free to users.

Equally, with Chrome able to work with ARM and x86 chips, the chief chip architectures currently in use, Google will have little difficulty in porting the OS from netbooks to both desktops and laptops.

Consequently for Microsoft the release later this year of Windows 7, the intended replacement for both Windows Vista and Windows XP, noticeably now eight years old, takes on an even greater significance. Any propensity to unexpectedly crash, any bugs, or any major security problems, and many users may prepare to migrate. For the first time they could have a viable alternative that will not require them to replace their hardware.

In defence, Microsoft is unlikely to hurry to produce a version of Office capable of running under Chrome. So anybody needing to work with Word, Excel or PowerPoint might find the transition more difficult. But, should Google choose, it clearly has both the resources and the technical capability to find a solution.

Such an attack on Microsoft in a territory it has always considered its own proprietary backyard poses far too great a threat to be ignored. As a result its primary corporate focus is likely to be on protecting its position, and this may divert attention from the promised launch of Windows Mobile 7, a firm release date for which has yet to be announced.

Supposed to finally bring Microsoft more in line with its competitors in offering consumer-friendly features WinMo 7 is, according to Microsoft Chief Executive Steve Ballmer, "an area of major excitement and innovation for the company as we move forward."

First though we have to contend with the interim release of WinMo 6.5 and Microsoft’s response to the iPhone’s App Store, the clunkingly christened “Windows Marketplace for Mobile”. It can only be hoped the new OS proves considerably less bloated than that mouthful of a name would suggest.

The next eighteen months are critical for Microsoft, its shareholders and employees. Should mobile really be the future of computing, WinMo 7 may arrive too late. If not, Google’s tanks are now parked on Microsoft’s lawn. Either way, few in Redmond will have too much time to celebrate when April 4 finally comes around.