The commercial version of the open source Xen virtualisation product, XenServer is what's referred to as a hypervisor. That means it can be installed and run directly on bare hardware instead of being loaded as an application on a Windows or Linux host, as is necessary with Microsoft's Virtual PC 2007 or VMware Workstation, for example.

That, so the theory goes, enables it to make better use of hardware resources (because there's no extra software to get in the way) and so deliver better levels of performance and scalability. Security, too, should be enhanced with no underlying OS vulnerabilities to worry about.

To run XenServer you need a host system fitted with Intel's VT or AMD-V processors, but that's not an issue as most servers and even many desktops now come with these as standard. Plus you can start with just one processor if you want, although up to 32 can be supported in total, along with up to 128GB of memory. As such XenServer can be used to satisfy a wide range of virtualisation needs from those of the small business to large corporate data centres.

Get the latest Dell Coupons and other computer coupons at CheapStingyBargains.com.

The software is remarkably easy to install with the core hypervisor supplied on a single CD with another optional disk if you want to support Linux VMs. Boot from the first of these and a Linux-like install routine takes you through the setup which, on our test server, took no more than 10 minutes.

Hardware support is much enhanced in the latest XenServer 5 release with native drivers for a wide range of local storage arrays, NAS appliances and SAN products. Fibre Channel and iSCSI technologies are both supported including the latest 8Gbps adapters from Emulex and QLogic.

With some other hypervisors you have to buy separate tools to manage more than one host. With XenServer, however, a Windows-based remote console (XenCenter) is included on the install CD plus there's now a local management console on the server, not just the command prompt found in previous versions. However, it's XenCenter you'll use most of the time, especially if you've more than one XenServer host to look after.

XenCenter takes a while to get to grips with, but creating new VMs and getting them running is pretty straightforward. The latest version also features a range of new tools to tag, group and generally organise virtual machines, plus issue email alerts to warn of host failures and problematic changes to VM setups.

Wizards and templates help with the creation of new VMs which can be configured with up to eight virtual processors and 32GB of RAM each. These can run most versions of Windows or Linux (32-bit or 64-bit in either case) including the latest Windows Server 2008, Windows XP SP3 and Vista SP1 releases. Support for the latest Red Hat and SUSE Enterprise Linux distros has, similarly, been added, together with a new XenConvert tool to migrate physical servers to the Xen VM format.

XenServer 5 is also particularly well served when it comes to high availability and disaster recovery options. With earlier releases you could already manually migrate live VMs between servers (XenMotion) but to this have been added tools to automatically migrate and re-start VMs when problems occur.

On the downside, these features are only available in the more expensive versions of the product, such as the Enterprise edition ($3,300 per server) which includes support for XenMotion and most of the automated high availability options, or the Platinum edition ($5,500 per server) which adds dynamic provisioning of workloads.

If you don't need these, however, the Standard edition starts at just $990 per server, with no processor /core limits. There's also a free Express Edition, limited to single server with just two processors, although with no VM or memory restrictions, making it a good choice for development and testing.

The latest commercial release of the Xen hypervisor, XenServer 5 has been much enhanced with native support for a wide range of storage sub-systems, an improved management interface and classy high availability and disaster recovery options, making it a production-class virtualisation solution.