There's nothing like a major platform upgrade to liven things up in the dog days of summer. This week sees the release of XenEnterprise v4, which marks XenSource's latest effort to prevent VMware from grabbing all the action in the red hot virtualization market.

All too often, new software versions deliver not much more than a few tweaks here and there and some added functionality. But not this time. Not only does v4 bring in a 64-bit hypervisor, but a range of new tools providing things like server resource pooling, centralized management, built-in connectivity to NAS, SAN and iSCSI environments, and a new set of open APIs for leading scripting languages.

While the list of upgrades is impressive, even Xen officials realize it's unlikely that features alone will put significant pressure on VMware, which is due to launch its own Virtual Infrastructure in the near future. That's why the company is leveraging its open source design to reach out to hardware vendors in the hopes of getting pre-loaded onto as many systems as possible. So far, they have brought in NEC, which will bundle XenEnterprise on its x86 servers.

But from a user perspective, how does XenEnterprise stack up against not only Virtual Infrastructure but the other virtualization platforms from SWsoft and Virtual Iron? CRN put all four systems onto Intel Duo and quad-core servers, ranking Xen second only to VMware, due primarily to a lack of software lifecycle management capabilities. Still, v4 was considered best for small and mid-size Windows environments, especially those running standard multitier applications.

When it comes to Linux shops, however, Xen is about to get a new competitor in the form of KVM. Like Xen, the Kernel-based Virtual Machine is supported in the Linux kernel, and the two are largely interoperable, but KVM execs are talking about adding paravirtualization capabilities and other features to possibly take Xen to the mat in a war over Linux APIs.

It's interesting to note that while VMware has emerged as the leading virtualization vendor, less than 10 percent of the enterprise market as embraces virtualization to any significant degree. There's still plenty of virgin territory out there, and a growing cadre of solutions looking to claim their stake.