Microsoft has delayed Windows Vista Service Pack 2 (SP2) by at least a month, and will now ship it to manufacturing sometime in May or June, according to a Web site that has accurately predicted Windows release dates in the past.

TechARP.com, a Malaysian Web site that correctly pegged the release dates for Vista SP1 and XP SP3 in 2008, said that Microsoft will deliver a release candidate -- the final test version -- of Vista SP2 in March, a month later than the site had predicted earlier. Also, Microsoft will send the service pack to OEMs and out for retail copy duplication at some point in the second quarter of 2009, not in April as originally thought.

Vista SP2 will be released for download from the Web at an undetermined date after Microsoft ships the service pack to OEMs. In the past, Microsoft has had both short and long lag times between the two dates.

Windows XP SP3, for example, was released to manufacturing April 21, 2008, and offered for download May 6, about two weeks later. With Vista SP1, however, it waited about six weeks after sending the update to manufacturing before it let the general public download the service pack.

Inserted into the Vista SP2 schedule, said TechARP, is something Microsoft's calling a "release candidate escrow build." According to the site, an escrow build is a version on which development has stopped, but is handed to developer and testers, who are asked to shake out the code one final time to make sure there are no show-stopping bugs.

Elsewhere, TechARP also said that computer makers will not be required to use Vista SP2 on new hardware, as is usually the case when the Microsoft wraps up a major update, such as a service pack. "OEMs will not be compelled to ship their systems with the new builds, which would have required extensive work [such as] tests, implementation and logistics," said TechARP. "They are also not required to send their customers the Service Pack 2 upgrades."

TechARP speculated that Microsoft will make Vista SP2 optional for OEMs because Windows 7, Vista's successor, may be hard on its heels. "Many OEMs are probably hesitant about spending more money and [putting more] effort into qualifying the new builds with their products, especially in light of the current economic situation," said the site. "So the onus will be on the consumer to update their Windows Vista via Windows Update."

Microsoft issued the first public beta of Windows 7 on January 10, but as of yet, has not set a timetable for the new operating system's release, other than to say it will hit the street by early next year.

Microsoft did not immediately respond to questions about Vista SP2's timetable.