Microsoft will support both Linux and Solaris in its next version of Virtual Server. But virtually, on top of Windows.

At the same time, the interim release of the product was renamed Virtual Server 2005 R2, rather than "Service Pack 1" because it will include significantly more changes than a usual service pack, said Zane Adam, director of marketing in the Windows Server division of Microsoft. The software giant typically offers service packs and interim releases called "R2s" between major updates to its server products.

Those "enhancements" include support for Linux and Solaris - technology that Microsoft is developing with the help of some of its partners, although Adam refused to say which.

Virtual Server 2005 R2 also will include 64-bit support, which allows more virtual machines to run on one server. It will feature better performance for virtual machines in memory-intensive applications, as well as higher availability through new clustering technologies, Adam said.

Microsoft introduced Virtual Server in October 2004. It allows virtualisation of the Windows Server OS so multiple instances can run simultaneously on one server. It competes directly with virtualisation technology available from VMWare.

Microsoft CEO Steve Ballmer first announced in April that Microsoft would include third-party support for Linux in Virtual Server. At the same time, he also announced Hypervisor, a technology that will add the virtualisation and management features of Virtual Server directly to the OS. Hypervisor will eventually be included in the next major release of Windows Server, codenamed Longhorn, due 2007.

At the time of the Hypervisor announcement, the fate of Virtual Server as a standalone product was widely questioned, but Microsoft said it would continue to add enhancements to the product and sell in as a separate server product.

Zane reconfirmed those plans Wednesday and said a new full release of Virtual Server will follow its R2 version. The beta of that release will be available in the first half of 2006, with full availability of the product scheduled for the second half, he said.