Windows execs Mike Angiulo and Steven Sinofsky show a prototype Windows 8 tablet for developers in September.

The big question for the past day on the Microsoft beat: What in the heck is the major, can’t-miss news that the company is promising to deliver on Monday?

Microsoft isn’t saying a word, despite endless attempts at arm-twisting from people like me. But overnight, a plausible answer emerged. The Wrap quotes an unnamed source saying that Microsoft will be unveiling its own tablet, based on the upcoming Windows 8 operating system, to take on the iPad. AllThingsD reports that it’s hearing the same thing.

Mary Jo Foley connects those reports to Microsoft’s Barnes & Noble partnership, and wonders if the real target might be Amazon’s Kindle Fire.

Whatever the case, it would be a huge break with tradition for the company.

Dating back to the very early days of the PC industry, Bill Gates and Paul Allen chose to stay out of the hardware business and instead supply the operating system and key applications for computers. It was the key strategic decision that led to Windows dominating the market for PC operating systems, in part because hardware companies knew that their OS vendor was a partner, not a competitor.

However, it wouldn’t be completely unprecedented for the company. Microsoft made an exception in the video-game business — deciding that coming out with its own console, the Xbox, was the only way to effectively compete with the likes of Sony and Nintendo. And the strategy has largely worked.

With the rise of the iPad taking the steam out of sales of low-end Windows-based computers, it’s quite possible that Microsoft has decided to make a similar exception in the tablet market, assuming these latest reports are true.

Whether a Microsoft-branded tablet would be an effective competitor to the iPad or Kindle Fire is another question entirely, depending on a whole range of factors, from the quality of the experience to the price.

Stay tuned for more on Monday.

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