Microsoft has given 15,000 testers a release candidate of Windows Vista Service Pack 1 (SP1), and said it is still on track to deliver the update early next year.

A new build of Service Pack 1 (SP1) dubbed Windows Vista SP1 RC Preview " incorporates feedback from users in our beta programme, including changes to the setup and installation experience," according to a Microsoft spokesperson.

The first beta of SP1 was seeded to approximately 12,000 testers about seven weeks ago, after considerable ship date speculation and several months of uncertainty whether the company would even produce its usual service packs for the new operating system.

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Windows Vista SP1 preview released

First look: Windows Vista SP1

"We will release a [release candidate] of SP1 to a broader group of testers soon," the spokeswoman added. "And we are targeting the first quarter of 2008 to release SP1 to manufacturing."

Microsoft, however, did not respond to other questions, including whether a pre-release version of SP1 would be offered to all comers.

Vista, which has received its share of criticism from users and reviewers, has been deployed by relatively few big businesses in the 12 months since it was given the green light by Microsoft. Results of a survey by Forrester Research, for example, said that only 7 percent of European and US companies will have started deploying Vista by the end of the year; that number, however, will climb to 32 percent by the end of 2008, a Forrester analyst added.

Although Microsoft is obviously extending the service pack concept to Vista - a fact that was unclear for several months after the operating system shipped to consumers in late January - it's also made much of several recent performance, stability and reliability updates that have been pushed to all Vista users. The most recent was added to the Automatic Updates lineup offered via the Windows Update service on Tuesday.

"Continuous improvement is the name of this game," said Nick White, a Vista program manager, in a posting on a company blog that described the three updates provided to all users this week.