Microsoft will attempt to bring the much-heralded promise of server virtualisation into the mainstream this summer, with the June release of Microsoft Virtual Server 2004 (MVS 2004).

Long familiar in the mainframe world, virtualisation allows one operating system to act as a host for a number of others, not necessarily of the same type. The technique has garnered a great deal of attention as a way to pool server resources and simplify management of workloads.

Microsoft hopes to make the technology more widely available with MVS 2004, a program based on technology acquired from Connectix and which will compete with the GSX Server product of virtualisation specialist VMware in the Windows arena. MVS could prove cheaper but it lacks the breadth of coverage of VMware's product. Microsoft has not yet announced licensing charges but its prices will have to be keen to undercut VMware's Linux-based offerings.

IT Week Labs tested a beta version of MVS 2004. The unfinished code ran only under Windows Server 2003, while the browser-based control console worked only with Windows XP. However, Microsoft said Windows 2000 Professional and Server will also be supported in the final release.

Microsoft hopes Windows NT4 and Windows 2000 Server users will deploy MVS to underpin a migration of existing applications to Window Server 2003.

MVS could allow Microsoft to extend support for NT4 at minimal cost, as the hosting process means that only one virtual hardware configuration needs to be supported. However, Microsoft said that support for NT4 running under MVS will cease at the end of the year along with that for conventional NT4 installations.

MVS is optimised for hosting Windows and, unsurprisingly, support for Linux virtual servers and applications will not be available from Microsoft.

However, Microsoft's Mark Tennant said hosting applications on virtual servers would not affect technical support for its enterprise applications such as Exchange 2003. Users that access an open source application such as Sendmail under MVS will still need a Windows 2003 Client Access Licence (CAL).

"If you have a long-term strategy to develop virtualisation through the datacentre, or if you are looking to manage complex server environments, then VMware is the better option," said Neil Macehiter of analyst Ovum. "If you are a firm using Microsoft, there may be cost benefits in opting for the Microsoft offering for wholesale desktop upgrades or revitalising server platforms."