Before the month ends, not a single new computer from Dell (Nasdaq: DELL) will be sold with Windows XP preinstalled, marking the beginning of the end of the operating system's dominance.

Through much of its nine-year history, Windows XP has been the most popular version of the most popular operating system in the world. As recently as August, research analysis company Net Applications reported that Windows XP was installed on 60.89 percent of all devices it tracked. Windows 7 and Vista were next in line at 15.87 percent and 14 percent respectively.

Yet despite this dominance, Microsoft (Nasdaq: MSFT) has started to set up Windows 7 as the successor. Net Applications said the operating system is the fastest-selling in history, at more than 150 million units since it became available in October of 2009.

Microsoft has made it clear that XP will be phased out. In July, the company stated that on Oct. 22 of this year, it will stop allowing original equipment manufacturers to ship any new computers with Windows XP preinstalled. Dell said it is getting a head start on this process.http:/

"Per Microsoft guidelines regarding Windows XP, system vendors like Dell will no longer be able to ship systems with XP Professional and XP Home after October 22, 2010. This means that we will stop offering XP as an option for customers starting this month in preparation for next month's deadline," the company wrote in a blog post.

For the most part, Microsoft ceased all sales of Microsoft XP in 2008. However, it has allowed assorted manufacturers to ship laptops and PCs in various emerging markets with the system preinstalled. It has also allowed enterprise customers the ability to downgrade to older operating systems in order to make the transition to Windows 7 easier. Microsoft has extended those downgrade rights throughout Windows 7's lifecycle.

"To support our customers' 'unprecedented move' to migrate their PC environment to Windows 7, we have decided to extend downgrade rights to Windows XP Professional beyond the previously planned end date at Windows 7 SP1. This will help maintain consistency for downgrade rights throughout the Windows 7 lifecycle," Windows spokesperson Brandon LeBlanc said in a blog post.

With the majority of its systems still running Windows XP, Dell said it will continue to offer XP Driver Support until December of 2012. Furthermore, the company has offered extensive guidelines for enterprise customers on how to transition from XP to Windows 7.

Microsoft Vista, which is the middle child of the group, has become more overlooked with each passing month. Not only did Windows 7 surpass it in usage in less than a year, Microsoft announced that it too will be phased out of all new computers. Microsoft said on Oct. 22, 2011, OEMs will no longer be able to sell PCs with Vista preinstalled.

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