The long march to the release of Windows Server 2008, aka Longhorn Server, continued on Monday, as Microsoft announced that it is making the first Release Candidate version of the upcoming operating system available for public download.

Microsoft said that RC0, as it's being called by the software vendor, will become available on its Web site within the next 24 hours -- replacing the Beta 3 release that it has been offering to early users.

RC0 is the first pre-release version to include a built-in virtualization hypervisor, which is code named Viridian. But Ward Ralston, senior technical product manager for Microsoft's Windows Server group, noted that the hypervisor component "is not yet in beta" and is thus less mature than the rest of Windows Server 2008.

Microsoft declared as long ago as April that the OS itself was basically "feature-complete." In contrast, the hypervisor, which will compete with technology from server virtualization market leader VMware, will still be in Community Technology Preview form when Windows Server 2008 ships in next year's first quarter, Ralston said. A finished version of the hypervisor will be ready within six months of the operating system's release, he added.

IT managers who have been testing earlier versions of Windows Server 2008 as part of Microsoft's Technology Adoption Program say they're largely impressed with the OS, though not without some reservations.

Robbie Roberts, IT manager at Windrush Frozen Foods, an Oxford, England-based fine foods importer, has been using Windows Server 2008 in live applications for the past two months to run his company's rights management services and its print servers as well as a portal based on Microsoft's SharePoint Server 2007 software.

With just a two-person IT team that oversees 25 Windows servers, Roberts considers automation and ease of use to be his highest priorities. Windows Server 2008 is delivering on both those counts, he said.

"The worst thing they could have done is totally redesign the [operating system] so that there would be a huge learning curve," Roberts said. Instead, "the user interface is cleaner while keeping it as similar as they could."

Small things, such as the ability to reduce the number of Windrush's domain controllers through the use of Windows Server 2008, also are helping to boost the performance of the company's servers, Roberts said.

He added that bugs haven't been an issue with the software. "We were involved in the Windows Server 2003 rollout, and we had tons of problems," he said. "We absolutely expected tons of problems with Windows Server 2008. But -- hand on heart -- we've had none. We found running Vista more difficult than Windows Server 2008."

The main problem Roberts did encounter was in getting SharePoint, in particular its Excel Services feature, to run properly with the new operating system. But that turned out to be due to a problem with SharePoint, he said.

Windrush currently uses VMware's virtualization software, and that product's "features and performance are great," Roberts said. "But I'm a GUI type person, so I don't like using the command line in Linux." He plans to try testing Microsoft's Windows Server Virtualization hypervisor as soon as he can.

Roberts also plans to move the rest of his Microsoft applications onto Windows Server 2008 as soon as possible, except for Office Communications Server, which he said is not yet supported by the operating system.