A month after Microsoft pushed back the beta release of the Windows Server virtualisation software, code-named Viridian, the company has dropped several key features to make its final deadline.

Saying "Shipping is a feature, too," the general manager of Microsoft's virtualisation strategy, Mike Neil, ticked off three features of Viridian that the development team cut from the upcoming add-on to Longhorn Server.

"We had some really tough decisions to make," Neil said. "We adjusted the feature set so that we can deliver a compelling solution for core virtualisation scenarios while holding true to desired timelines."

Microsoft dropped live migration, which lets users shift running virtual machines between physical servers; the ability to add storage, processors, memory or network cards on the fly; and it pulled processor support back to a maximum of 16 cores, such as a server with four quad-core CPUs or a box with eight dual-core chips.

"We [will be] postponing these features to a future release of Windows Server virtualisation," Neil said. He did not offer a timetable for that release.

Only last month, Neil postponed Beta 3, the first public beta of Windows Server virtualisation, from the first half of the year to the second half. At the time, he cited performance and scalability goals as reasons for the delay.

Neil said Beta 3 would be ready for downloading when Longhorn Server went to manufacturing; the final virtualisation code was expected to ship within 180 days of Longhorn's launch.

The feature retreat was something of a deja vu. Windows Vista became notorious for gradually shedding features to make its late-2006 release to businesses. "This is somewhat typical of them, this little slip by slip," analyst with Directions on Microsoft, Michael Cherry, said. "It's the death by a thousand cuts.

"So the question has to be, is this just the first of many [feature] slips, or the only one?"

VMWare, which unveiled a new version of its Workstation 6 hypervisor this week, already had a large lead over Microsoft in virtualisation. With this delay, the gap gets bigger. "Without these features [in Windows Server virtualisation], it makes VMware secure that much longer. Microsoft definitely has some catching up to do," Cherry said.

The cutbacks, along with the already-announced delay in Beta 3's release, were disappointments to users, Cherry said, but they might have an even larger impact on Microsoft. "This may delay some people's adoption of Longhorn," he said.

Still, Microsoft was making a smart, if tough, decision, he said. "It's hard to get too upset, since in many ways they're doing the right thing," Cherry said. "It's better to let it slip than produce a poor product."