Enhanced ARM support and stronger scalability for cloud computing servers highlight the long list of new features in Xen 4.4, the open source virtualization hypervisor whose release the Linux Foundation has announced.

Xen offered some ARM support before, but it is much more comprehensive in the latest version. Now, the hypervisor supports all of the following ARM platforms: AppliedMicro’s X-Gene, the Arndale Board, Calxeda ECX-2000, TI OMAP5 and the Allwinner SunXi boards. It also features support for 64-bit guests on ARMv6 systems, as well as userspace tools for creating and managing virtual machines that are "64-bit ready" in ARM environments.

Xen 4.4 also introduces a new event channel implementation, developed by the XenServer team at Citrix (CTXS), that allows the hypervisor to run thousands of guests on a single bare-metal server. That enhancement, the developers say, will be important for driving continued evolution in the open source cloud by enabling more scalability and allowing administrators to take advantage of larger physical machines.

Meanwhile, Oracle (ORCL) has contributed a new virtual mode for Xen, called PVH, that is available in Xen 4.4 as a "functional preview." It provides paravirtualization support, allowing Xen to take advantage of some of the virtualization extensions available on host CPUs.

These are only the headlining updates in the new release, which also introduced performance enhancements for storage devices, better diagnostics and debugging and Spice protocol support to simplify the sharing of clipboards and other resources between guest and host machines.

In many ways, KVM, another open source hypervisor, remains the darling of the open source community, with its tight integration with the Linux kernel and strong support from the Linux Foundation through the Open Virtualization Alliance. But Xen remains an important contender in the virtualization world as well, and it enjoys support from the Linux Foundation as a collaborative project. With its sights set on ARM and low-power servers, Xen appears to be carving out a somewhat different niche to distinguish itself from KVM.