Xen getting multiprocessor support

Xen is a 'hypervisor' -- a thin layer of software that governs how different operating systems get access to computer resources such as processors and memory. But the current version is hobbled by the fact that each operating system can use only one processor.

Version 3, which programmers hope to begin testing this month, will lift that limit, said Ian Pratt, a founder and lead programmer of the open source project and the company XenSource that's trying to commercialise it. "We hope to get 3.0.0 out in August -- sooner if we're ready," Pratt said, though he cautioned, "I'm a firm believer in having releases driven by product quality rather than dates."

The multiprocessor support is important, said Illuminata analyst Gordon Haff. "Some applications obviously need more than one processor's worth of performance," he said, and Xen also stands to benefit from not being pigeonholed as software with only limited abilities.

Running multiple operating systems on a single machine -- an ability that Unix servers and mainframes have had for years -- is useful for several reasons. It makes it easier for one server to share multiple tasks and therefore replace several independent machines. And personal computers can be divided into noninterfering domains for business use, personal use or systems management. Mainstream adoption of multi-OS practices  will probably be hastened by features in Intel processors this year and Advanced Micro Devices chips in 2006 that make the task significantly easier.

Xen has gained active help from Intel, IBM, AMD, Hewlett-Packard, Sun Microsystems, Red Hat and Novell. In prevailing industry argot, its job is to virtualize computer resources, letting operating systems run in separate 'virtual machines', often called partitions, rather than directly on the hardware itself.

But Xen also has rivals to fend off. EMC subsidiary VMware has a head start of years, already supports virtual machines that use up to two physical processors, and will receive four-processor support by the end of 2005. And Microsoft is working on its own hypervisor, a product expected to ship in 2007.

Another potentially formidable competitor could have been IBM's rHype, or Research Hypervisor, given that Big Blue has decades of experience with the technology. But in a mailing list posting, an IBM programmer said the project -- or at least the version for Intel chips -- "was mostly for demonstration purposes" and steered people toward Xen.

Xen uses an approach called paravirtualisation that stops a step short of the full-on virtualisation used by market leader VMware. That approach boosts performance, Pratt and analysts agree, but today requires that operating systems be modified to take advantage of it. The top Linux sellers, Red Hat and Novell, have released test versions of their open source operating system products with tentative support.