The service pack includes all updates issued since Windows XP Service Pack 2 was released in 2004, and some new elements.
Microsoft on Monday said it has finished work on the third and final service pack for its Windows XP operating system and that the update will be available for public download on April 29.
Windows XP, Service Pack 3, will be released to Microsoft business customers through their MSDN and TechNet subscriptions sooner than that -- but Microsoft didn't provide a specific timetable.
"Windows XP SP3 bits are now working their way through our manufacturing channels to be available to OEM and Enterprise customers," a Microsoft staffer said on a company blog Monday.
The service pack should offer a number of enhancements over the current version of the OS. It includes all updates issued since Windows XP Service Pack 2 was released in 2004, and some new elements.
Among them: A feature called Network Access Protection that's borrowed from the newer Windows Vista operating system. NAP automatically validates a computer's health, ensuring that it's free of bugs and viruses before allowing it access to a network.
Windows XP SP3 also includes improved "black hole" router detection -- a feature that automatically detects routers that are silently discarding packets. In XP SP3, the feature is turned on by default, according to Microsoft.
Windows XP SP3 also steals a page from Vista's product activation model, meaning that product keys for each copy of the operating system don't need to be entered during setup. The feature should prove popular with corporate IT managers, who often need to oversee hundreds, or even thousands, of operating system installations.
Microsoft is in a bit of a Catch-22 with XP. The more it strengthens the OS, the less reason users have to upgrade to Vista, which by many accounts has failed to catch on with computer users in both the home and office since it debuted last year.
Microsoft recently released Windows Vista Service Pack 1, which includes more than 300 hot fixes designed to improve the operating system's speed, security, and stability. Many users, however, have complained that installation of Vista SP1 on their systems caused numerous problems.