The newest Windows Vista Service Pack 1 Release Candidate can be downloaded by anyone who wants to try it, after Microsoft has decided to make it public.

Microsoft initially intended to make the new version, called Windows Vista SP1 RC Refresh, available only for beta testers.  

Microsoft announced that in order to install the Windows Vista Service Pack 1 RC Refresh, the users must uninstall Vista SP1 Release Candidate, the earlier version offered to the general public a month ago.

Microsoft warned that Windows Vista SP1 RC Refresh is for individuals, organisations, and technical enthusiasts who are comfortable evaluating pre-release software and is provided for testing purposes only.

The new version of the update shouldn’t be installer on primary or mission critical systems and Microsoft recommended a full backup of the data to installing the software. Windows Vista SP1 RC Refresh will no longer operate after June 30, 2008.

Windows Vista Service Pack 1 is the first major update issued since the launch of Microsoft’s latest OS, one year ago.

According to Microsoft, Windows Vista SP1 will not add new features, but instead it will address key feedback received from its customers. In addition, the company insisted that the SP1 would not affect any applications that are currently running on Windows Vista.

Amongst other things Vista SP1 will enhance BitLocker Drive Encryption (BDE) by offering an additional multifactor authentication method that combines a key protected by the Trusted Platform Module (TPM) with a Startup key stored on a USB storage device and a user-generated personal identification number (PIN).

In addition, the update will add support for upcoming standards and hardware, such as Direct3D 10.1, Secure Sockets Tunneling Protocol (SSTP), Extensible Firmware Interface (EFI), and the Extended File Allocation Table (exFAT), a file system for Flash drives.

The service pack will include support for Secure Digital (SD) Advanced Direct Memory Access (DMA), which will be on compliant SD host controllers soon, to improve transfer performance and decrease CPU utilization.

Microsoft confirmed that it is on track to deliver the Windows Vista SP1 in the first quarter of 2008 as promised.

Last week, during his speech at CES, Bill Gates, Microsoft Chairman, announced that his company sold more than 100 million licenses of Windows Vista since the launch.