The first public beta of Vista SP2 was released to the general public in December 2008, but the latest release - known as the RC-Escrow build - was made available to a restricted group of testers, alongside a similar test version of Windows Server 2008 SP2.
An Escrow build indicates that development work on the code has ceased, and that the focus has shifted to fixing bugs ahead of release.
According to sources, the Release Candidate is now expected in February, with the official availability of the service pack coming sometime in the second quarter of 2009.
Vista SP2 contains all the updates made available since SP1, which was released in March 2008. It also contains changes to support new types of hardware and some emerging standards, according to Microsoft.
These include Windows Search 4.0, which promises improved relevancy and faster searching, Blu-ray support, Bluetooth 2.1 Feature Pack, Windows Connect Now to simplify Wi-Fi configuration, and support for UTC (Universal Time Coordinated) timestamps in the extended FAT file system.