Microsoft will phase out Windows XP as an option for brand-name computer makers faster than it has any other operating system, but an analyst said it probably wasn't a decision made to pump up Vista revenues at XP's expense.

According to Microsoft's posted timetable, the company will stop licensing Windows XP to OEMs and terminate retail sales of the operating system 31 January, 2008. The time between the general availability of XP's successor, Windows Vista, and that drop-dead date is just 12 months.

By comparison, Windows 95 was terminated 30 months after Windows 98's debut, which in turn had an 18-month run after the release of its heir, Windows Millennium. On the business side, Windows NT Workstation 4.0 was available to OEMs for 26 months after Windows 2000 Professional appeared; that OS lived 27 months on the OEM list after Windows XP Professional made it to market.

Users shouldn't read too much into Windows XP's shortened lifespan, said Paul DeGroot, an analyst with Directions on Microsoft, a research firm. "Certainly they want to push Vista, but I don't see them forcing this on the market. A bigger motivation, I think, might be to simplify things, to avoid having two different fulfilment SKUs in the marketplace."

Another reason for the shorter cycle, said DeGroot, is the much longer span between the release of XP and Vista, compared to the relatively short periods between earlier versions of Windows. "You're looking at more than five years" between XP and Vista; the gap between the release of Windows 2000 and XP was less than two years.

When total time on the OEM and retail lists is tallied, Windows XP comes out smelling sweet: it was available at retail and to OEMs for 73 months, two months longer than Windows NT Workstation 4.0, and 25 months longer than Windows 2000.

"Microsoft wants to indicate to the marketplace, and ISVs [independent software vendors] in particular, that Vista compatibility is something they should be working on today," DeGroot said. "I see this as them encouraging the partner ecosystem to make sure that they're working on Vista compatibility now."

Even the shorter life-cycle before Windows XP is scratched from retail and OEM licensing won't really affect two of the PC market's major buying groups, said DeGroot. Consumers, for instance, not only typically take what's on the shelves without questioning, but Microsoft's emphasis on security is "a good argument for Vista for consumers," DeGroot said.

"And this shouldn't have much impact on the business community," he said. "Business customers have downgrade rights because they buy through volume, and most already own XP volume media" that they can use to substitute for Vista after January 2008.

Small business is the group that may be at the most risk of disruption, DeGroot said, because those companies often buy PCs from OEMs or at retail, but may not have downgrade rights to, for example, dump Vista for Windows XP.

"I don't think this is a grab for cash," said DeGroot. "At the most, it's a happy coincidence."

The decision to cut off OEMs from XP next year may seem odd in light of a move by Microsoft this January that extended support to Windows XP Home and XP Media Center to match Windows XP Professional's dead-end of April 2014. Windows Vista Home Basic, Home Premium, and Ultimate, meanwhile, will see all support end two years before that, in April 2012.

Microsoft did not reply to a request to explain why it will have XP on the OEM list just 12 months after Vista's retail roll-out.