Implementing a move that's been planned for months, Microsoft will no longer make Windows XP available to large computer makers, such as Dell, Lenovo, or Hewlett-Packard, or to software retailers, after June 30. It will continue to offer the OS to "system builders," that is, small, independent PC makers, through July of next year.
Microsoft also said it would make Windows XP available to builders of ultra-low-cost PCs and laptops, such as Asus, until 2010. It's widely seen as an attempt to prevent Linux from establishing a beachhead in emerging markets.
Also, some PC makers, including Dell, are giving customers continued access to XP for an indefinite period if they buy certain models of Vista-based computers. A loophole in Microsoft's licensing terms lets users of its most current operating system "downgrade" to a previous version at no additional cost.
For the most part, however, Monday marks XP's last official day on the market after a seven-year run, as Microsoft ceases bulk shipments and retail sales of Windows XP Professional, Home, Media Center, and Tablet PC edition.
Some XP diehards aren't giving up their OS without a fight. A petition to save XP launched by a computer industry publication has so far drawn more than 210,000 online signatures.
Fueling the fight is the fact that many computer users have given XP's successor, Windows Vista, the thumbs down. Many have balked at Vista's cost, resource requirements, and lack of compatibility with older software.
Acknowledging that many customers won't be moving off XP anytime soon, Microsoft recently said it would extend support for the OS until 2014.