Microsoft has released a new test version of Windows Vista Service Pack 1 (SP1), and promised a wider group of testers would get their hands on the latest update.

Initially, though, only about 15,000 invitation-only testers will be able to download Release Candidate 1 (RC1) of Windows Vista SP1. Microsoft released the RC1 installation file to that group yesterday. They also were the only testers who were able to download an earlier batch of release candidate code, called Vista SP1 RC Preview, that was made available to them last month.

Subscribers to Microsoft's MSDN and TechNet services, who number in the hundreds of thousands, will be able to download the RC1 software today, according to David Zipkin, a senior product manager at Microsoft. He said that the code will become "fully public" by next week. The RC1 code weighs in at 60MB for a single-language version, Zipkin added.

Earlier this week, Microsoft announced that in Vista SP1, it plans to do away with its so-called antipiracy kill switch - officially, a reduced-functionality-mode feature that was designed to take effect if users didn't activate the operating system with a valid software licence key within 30 days of installation.

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But Zipkin said yesterday that the antipiracy mechanism couldn't be removed in time for the RC1 release. Microsoft plans to ship another release candidate that won't include the reduced functionality mode before Vista SP1's commercial release in next year's first quarter, he said.

Although Microsoft said in October that more than 88 million copies of Vista have been shipped on PCs or sold at retail, the operating system has yet to be taken up in a big way by enterprise users in the 12 months since it was made available to them.

Vista SP1 won't offer many new features to users, according to Microsoft officials. Instead, the update is focused on under-the-hood improvements designed to fix Vista's nagging performance problems.

For instance, some Vista users have complained about long startup, shutdown and application load times compared with Windows XP, the operating system's predecessor. In addition, there have been complaints that Vista performs various computing tasks no faster, and in some cases slower, than Windows XP does. And users have also criticised the operating system's lack of support for third-party software and peripheral devices.

Zipkin said that some of the upgrades in Vista SP1 include improvements of up to 45 percent in copying files, plus faster resume, standby and hibernate times and speedier unzipping of compressed files. "Beta testers do like the performance," he said, although he added that it remains "too early" to do specific benchmarks comparing Vista SP1 with the initial release of the OS or with Windows XP.

By contrast, an outside testing company that got its hands on the RC Preview version of Vista SP1 said last month that the software didn't perform significantly faster than the original Vista release on a series of tests, and that it ran considerably slower than the upcoming Service Pack 3 update for Windows XP. A Microsoft official criticised the testing last week, saying in a blog posting that with the Vista SP1 code still under development, any benchmarks are "a moving target".

As part of Vista SP1, Microsoft also is trying to make it easier for IT managers, especially ones at multinational companies, to install the operating system. Zipkin said that the service-pack update will be available in standalone installer packages supporting either five or 36 languages, enabling systems administrators to use a single installer file to deploy Vista SP1 for end users in different countries.

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