Microsoft is watering down its upcoming Viridian virtualisation technology in an effort to maintain its original release schedule. 

The virtualisation software is scheduled to ship next year as an update to Windows Server, codenamed Longhorn, which is scheduled to ship by the end of this year.

The technology will no longer offer live migration, a feature that allows users to move virtual workloads to a different physical server as they are running.

Users will also not be able to add storage, networking resources, processors or memory to running servers. Virtualisation will support only up to 16 cores, whereas the original design promised 64.

Mike Neil, Microsoft's general manager for virtualisation strategy, said on a company blog that pulling the features allows Microsoft to maintain its planned launch schedule. 

"Windows Server virtualisation is a core OS technology for the future, and we chose to focus on virtualisation scenarios that meet the demands of the broad market: enterprises, large organisations and mid-market customers," he wrote.

The decision is the second set-back for Viridian within a month. Microsoft was forced on 12 April to delay the release of the Viridian public beta to the second half of this year.

The final product has been promised within 180 days of the Longhorn launch. Microsoft blamed the earlier delay on the technology's inability to run well on systems with 64 processors.

Microsoft boasted at the time that none of its competitors was able to match this level of scalability.

This statement was incorrect, however. Sun Microsystems' Solaris operating system runs on servers with 144 cores, and Novell's SuSE Linux Enteprise Server 10 is running virtualised systems with 512 processors.

Scaling back to 16 cores even puts Viridian behind VMware's ESX Server, which supports up to 32 cores.