Today most cloud-computing providers use the open source Xen hypervisor as their virtualization backbone. But users may increasingly gravitate toward commercial options -- some of which, in fact, are based on Xen's open source code -- such as Citrix XenServer. These offerings provide out-of-the-box capabilities and attractive management features that users have deemed worth the price. As more providers move into the cloud, they too may choose a packaged hypervisor that facilitates management tasks and alleviates the burden of writing code with open source Xen.

Consider Singapore Computer Systems (SCS). A channel partner of Citrix Systems and the managed service provider for grid computing services for Alatum, Singapore's largest commercial grid computing platform, SCS recently chose Citrix XenServer virtualization and support for its Platform as a Service offerings.

Why XenServer?
SCS' grid infrastructure is built on a scalable and redundant architecture and promises 99.9% availability. It has more than 2,400 CPU cores and 16 TB of usable storage to support thousands of customers simultaneously, according to Lim Jee Yen, the director of grid computing at SCS. Thus far the company has deployed XenServer on 200 physical servers with between four and eight virtual machines per physical server, Yen said.