Microsoft plans to ship Windows Vista Service Pack 1 in the first quarter of 2008, the company revealed in a posting on its Windows Vista Blog.

The software is currently available as an unofficial closed beta which has already surfaced on BitTorrent.

An official beta is slated for release in the coming weeks, but will not be available for general download. Subscribers to the Microsoft Developer Network and Microsoft TechNet programmes will get access to a pre-release version later this year.

Microsoft traditionally uses service packs to distribute security patches and performance and reliability updates to its applications.

Users can expect faster file copying and archive extractions, for instance, as well as shorter wake-up times from the hibernate and resume modes.

Internet Explorer has been optimised to offer better performance with JavaScript applications, and Microsoft also promises better reliability for systems that have been upgraded from Windows XP to Windows Vista.

Vista SP1 will not deliver any new features, but will add support for new types of hardware such as the Extended File Allocation Table, a new file system that allows for easier transfers between mobile devices and a PC.

The update will also bring Windows into the world of the Extensible Firmware Interface. The Bios replacement was scheduled to be part of the original Vista release, but was pulled in early 2006.

Vista's BitLocker drive encryption technology will be improved, allowing it to encrypt not only the C-drive but any additional hard drives or disk partitions beyond that.

Service Pack 1 is considered an important release for Vista because it marks a level of maturity and stability for the software. Many companies, including Intel, have indicated that they will not deploy the software until the Service Pack 1 release.

In related news, Microsoft also said that it plans to release Windows XP Service Pack 3 in the first half of 2008.

The update will deliver a small number of updates as well as a rollup of previously released updates for XP, including security updates, out-of-band updates and so-called hot-fixes.

A detailed description of Windows Vista Service Pack 1 is available in the Windows Vista Service Pack 1 Beta White Paper.