VMware will next week make its ESX 3i hypervisor available for free, a move the company is presenting as a logical step in growing the virtualisation market, but which some experts also see as necessary to counter the threat from rivals such as Microsoft.

Available since the start of this year, ESX 3i is a compact 'bare metal' virtualisation layer that runs directly on server hardware. Vendors such as Dell, Fujitsu-Siemens, HP and IBM offer it embedded into some servers and it is also available separately, but until now it has cost $495 (£247) to licence.

For firms using virtualisation in their datacentre, servers with embedded ESX 3i make it easy to expand capacity, and the move now means this costs them nothing beyond the hardware purchase.

"As soon as you throw that box into the datacentre, it becomes part of your virtual infrastructure," said Reza Malekzadeh, senior director of product marketing for VMware in EMEA.

But ESX 3i is simply a bare hypervisor, and companies need additional tools to build an effective virtualisation strategy that includes disaster recovery, consolidation, and load balancing. Malekzadeh said that making the hypervisor free is thus the next step in VMware's strategy to drive take-up of virtualisation.

"We have delivered free tools like Player and Server in the past, when the time was right," he added.

Butler Group analyst Roy Illsley said that while VMware's strength lies in its virtual infrastructure products, these are built on top of its own hypervisor and so it needs to get this technology adopted as widely as possible. The current move can thus be seen as a strategic one to counter the threat rivals such as Citrix and Microsoft might offer in future.

"If Windows Server 2008 is as popular in three year's time as [Windows Server] 2003 is now, people will start to re-visit their virtualisation strategy and ask why they need VMware if there's a hypervisor built into the operating system," he said.

While Windows with Hyper-V cannot match the capabilities of VMware's products today, it may well be able to in the near future, according to Illsley.