NEW YORK ( TheStreet) -- This is an article about the Windows 8 operating system for the PC and tablet, not for the phone.

Windows Phone 8 is a separate discussion, and you can find my initial opinion about that operating system in "Windows Phone 8 Review: Good, But Not Good Enough."

For several months, I had been very negative on Windows 8 for the PC, but I recently changed my mind. Today I'll explain why.

My impression had been very negative because I'd been playing around with Windows 8 on old, non-touch-screen hardware -- basically Windows 7 laptop and desktop computers that had been upgraded to beta versions of Windows 8 in various stages beginning in February.

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Using Windows 8 on a non-touch PC is a major pain. The new tiles and menu/touch-points do not lend themselves to a trackpad or mouse. Why? Because you have to hunt from side to side, from corner to corner, and that is an exercise in frustration. Beta-user feedback seemed overwhelmingly negative, confirming my own experience.

But then on Oct. 25 and 26, something happened. For the first time, I got to use both desktop/tablet versions of Windows 8 on purpose-built touch-screen hardware. As it turns out, this made all the difference.

Practically, how does this work? The point here is that as a user, you will be spending most of your time in the major Office apps (Outlook, Word, Excel, PowerPoint), a browser and some other apps you may use such as Skype and Apple's ( AAPL) iTunes. When you use most of these apps, you will not need a touch screen. You will use a trackpad or mouse just as would with Windows 7.

However, when you switch apps -- and, more importantly, when you start the computer -- you will find that you prefer to use the touch screen. It's just faster, easier and more logical that way. That's why a touch screen makes all the difference in terms of Windows 8 being an acceptable platform.

In other words, you will be spending 99% of your time in Windows 8 using a trackpad/mouse as usual. The problem is that if the other 1% is dysfunctional, it completely ruins the experience for the other 99%. As a result, you should at all cost avoid running Windows 8 on a non-touch-screen PC. Without a positive 1%, the other 99% will be miserable.

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