Microsoft on Monday released Windows XP Service Pack 3 to manufacturing and said that it will be available for download April 29.

Microsoft most recently issued an XP service pack -- XP SP2 -- more than four years ago.

The new service pack offers a range of upgrades to the current version of the operating system (OS). According to Microsoft, it includes all updates issued since Windows XP Service Pack 2 was released in 2004, plus a few new features.

These include what the company calls Network Access Protection (NAP), a feature appropriated from the latest version of Windows, the Vista operating system. NAP automatically audits the PC's "health" to ensure it is free of malware before allowing it access to a network.

Windows XP SP3 will also ship with enhanced "black hole" router detection. This feature automatically detects routers that are silently discarding packets. This is turned on by default in XP SP3, according to Microsoft.

In addition, the latest service pack will make use of Vista's product activation model, which does not require typing product keys for each copy of the OS during setup. The feature is targeted to corporate IT managers who often perform hundreds or thousands of installations of the OS.

Because Windows XP is so widely used in enterprise environments, the release of XP SP3 is likely to significantly slow down the deployment of Vista, experts contend.