The following commentary comes from an independent investor or market observer as part of TheStreet's guest contributor program, which is separate from the company's news coverage.

NEW YORK (

Trefis

) --

Microsoft

(MSFT) - Get Report

will launch the next version of the Windows OS -- unsurprisingly called Windows 8 -- in 2012. Windows has traditionally been one of the largest revenue generators for Microsoft and accounts for more than 25% of the total Trefis price estimate for Microsoft.

Windows 7 was launched back in 2009 and has since sold more than 400 million copies. However, its sales have been slowing and Microsoft's revenues from Windows dropped 2% last year. With Windows 8, Microsoft expects even more sales as it will support not only desktops and laptops but also tablets. In addition, Microsoft will roll out its App Store for Windows 8 concurrently that we believe holds sizable potential if it gains traction.

Apple

(AAPL) - Get Report

is its only major competitor in the operating system space with its Mac OS X offering.

We currently have a

$28 price estimate for Microsoft, which implies a 10% to 15% upside to the market price.

In a blog post about Windows 8, Steven Sinofsky, President of the Windows Division at Microsoft, confirmed that Microsoft will be launching a Windows App Store for Windows 8.

Apple launched its iPhone App Store in 2008, and it has been a huge hit. Apple recently announced that it had paid out more than $2.5 billion to app developers. Accounting for its 30% cut, it means that Apple made more than $1 billion from the App Store. Apple also recently launched a Mac App Store for its desktop users.

Apple currently has more than 200 million iOS users. The average price of an iOS app is close to $1.99.

We expect Microsoft to sell at least 400 million copies of Windows 8 in a year of its launch. We discussed recently where

we highlighted that Windows 8 will be the single most important driver to Microsoft's stock next year.

The expected average price of a Windows app would also be considerably higher than iOS apps. Accounting for all this, we think that the Windows 8 App Store could easily become one of Microsoft's billion-dollar businesses, causing the Windows division to become even more profitable.

Check out our complete analysis of Microsoft.

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This commentary comes from an independent investor or market observer as part of TheStreet guest contributor program. The views expressed are those of the author and do not necessarily represent the views of TheStreet or its management.