REDMOND, Washington (AP) - Microsoft Corp. said it will keep selling its Windows XP operating system beyond January, in response to demand from customers.

The company decided to extend the deadline until the end of June to give customers - particularly small businesses - more time to switch to the new Windows Vista.

"Maybe we were a little ambitious to think that we would need to make Windows XP available for only a year after the release of Windows Vista," said Mike Nash, a corporate vice president for Windows product management at Microsoft.

While software retailers and major computer makers like Dell Inc. will stop offering XP next June, system builders, or smaller companies that make and sell PCs, will still sell the older operating system until the end of January 2009.

Nash said Microsoft's policy in the past has been to discontinue an old operating system four years after its launch. But because Vista reached consumers more than five years after XP, the company had to revise the rules.

"Making it available through June was a little bit better" for customers, Nash said.

In April, Dell, which had all but stopped selling XP to consumers, said it would bring back more XP machines after customers asked for it. At the time, Microsoft responded that only "a small minority of customers" were still interested in the old operating system.

Microsoft is also extending the availability of a version of XP aimed at customers in emerging markets, Windows XP Starter Edition, until June 30, 2010.