By CEO Steve Ballmer's own description it is the one of the top three major events in the company's history, grouped with IBM PCs adopting MS-DOS and the advent of Windows 95.
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By that measure, if it's a flop it's huge.
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Windows 8 drives users crazy. It's a two-headed operating system that supports the traditional Windows keyboard-and-mouse interface as well as a touch-centric UI that many say is baffling, at least initially.
Then toss in a separate version of Windows 8 called Windows RT. It's a hardware/software bundle based on ARM processors that doesn't support traditional Windows x86 apps -- only so-called Windows Store applications that rely mainly on touch. Confusion reigns.
A version of the traditional desktop remains in Windows 8, but it's different enough to be uncomfortable. Users want an OS that builds on the past, not one that reinvents itself entirely. They lament the loss of the Start button and Start Menu upon which they relied.
When learning the Windows 8 touch interface they find it difficult to find and remember, say, how to turn the machine on and off, close applications, remove applications, switch among four or five apps running at the same time, find Charms, figure out what Charms are, etc., etc. It's a near-perfect storm of consternation and frustration.
Meanwhile the company's traditional PC market is being threatened by devices running Linux, Android and OS X even as sales growth of traditional PCs gets slower and slower, apparently headed for decline. That's Microsoft's bread and butter.
Compounding the problem, tablets and smartphones are gaining popularity as personal and business productivity platforms and arguably represent the main force undercutting traditional PCs. Microsoft comes in a distant third in both areas.
Windows 8 is supposed to help Microsoft make gains in these areas. But given its slow start so far and comparing it to the wild success of every version of iPad that ever launched, then Windows 8 is lining up to be a disaster.
So what was Microsoft thinking?