Microsoft Corp yesterday ceased selling its Windows XP operating system to retailers and major computer makers, despite protests from a slice of PC users who do not want to be forced into using the XP's successor, Vista.

Once computers loaded with XP have been cleared from the inventory of PC makers such as Dell Inc and Hewlett-Packard Co, consumers who cannot live without the old operating system on their new machine will have to buy Vista Ultimate or Vista Business and then legally "downgrade" to XP.

Microsoft will still allow smaller mom-and-pop PC builder shops to buy XP for resale through the end of January. A version of XP will also remain available for ultra-low-cost PCs such as the Asus Eee PC.