The virtualisation of computing resources has become a growing trend within IT departments because of the ability it offers to consolidate, reuse and extend physical computing resources in the enterprise.
But in a growing market that attracts a variety of new entrants all the time with many different approaches, it can be difficult for IT managers to evaluate what virtualisation could do for their businesses, and the implication in terms of configuration and pricing.
VMware may still be the dominant supplier in this space, but what do emerging players offer? And how do they fit into IT infrastructures?
According to a report by analyst firm Forrester, hardware suppliers and systems integrators are winning a lot of deals off the back of VMware, the leader for x86 server virtualisation.
"But now, Microsoft, XenSource and others are building viable alternatives," the report said.
"Forrester believes that a critical mass of enterprises will switch from x86 virtualisation projects to virtualised infrastructure strategies over the next two years, driven by VMware's technologies," said the report.
According to Forrester analyst Frank Gillett, by the end of 2006 51% of enterprises had deployed or piloted some kind of x86 virtualisation in their infrastructures. However, very few of these had moved onto wide-scale deployments.
Analyst firm IDC said VMware holds 85% of the virtualisation market, and has set the bar in terms of the potential for controlling the ever-increasing hardware cost, consumption and requirements necessary to satisfy more sophisticated and demanding application needs.
VMware was also the first supplier to remove the need for processor or operating system changes when carrying out virtualisation techniques on PC-based standard components.
The VMware ESX hypervisor-based version of its server virtualisation product released in 2001 offered IT organisations the opportunity to consolidate a number of physical servers into virtual machines running on a single physical instance, which is still available in the current VMware Infrastructure 3 Enterprise suite.
Since then, it has developed a vision it says will see hardware, software and operating system requirements managed through an entirely virtualised IT management infrastructure.
The growing commoditisation of the x86 server market is offering IT departments the opportunity to move beyond using virtual machines in just a development and testing role, to providing business critical application and back-up resources.
In August, VMware's initial public offering (IPO) doubled its share price on its first day of trading, potentially raising more than £447m in capital. So, for those who think virtualisation is only about server consolidation, perhaps they should think again.
Chip developments such as Intel Virtualisation Technology (VT) and AMD Virtualisation (AMD-V) are designed to accelerate virtualisation performance in the area of processor throughput, memory and I/O sharing.
These technologies by the top two chipmakers suggest anticipation of the x86 environment supporting evermore high-performance virtualised infrastructures.
However, Gillett points out that while VMware is taking advantage of Intel and AMD's hardware-assisted virtualisation technologies to boost support in CPUs, so are its emerging competitors, essentially bypassing "the painstaking engineering VMware originally had to create without CPU support," he said.
Start-up XenSource is one such emerging competitor snapping at the market leader's heels. Its open source, cross-platform approach touts the benefits of hardware-assisted virtualisation. This runs on both Intel VT and AMD-V chips, which gives near non-virtualised hardware speeds in terms of performance and response times.
This approach has the benefit of also offering standard Linux operating system hardware and drivers to local and fibre storage area networks.
XenSource also signed an original equipment manufacturer (OEM) agreement in July with Symantec for unified storage and server virtualisation capabilities. Storage virtualisation offers the ability to pool many different types of physical storage and manage them as logical data pools that can be allocated to applications, services and disaster recovery or back-up plans.
The Xen hypervisor technology, currently sold in the XenSource version 4 product family, has proved an attractive entry into this market for networking supplier Citrix. Citrix followed VMware's IPO a day later with the announcement it was acquiring XenSource for £248.3m.
Peter Levine, XenSource chief executive, said at the time, "This move is not about competing for the 5% of the market that is already being served. It is about steering into the 90% of white space that is wide open, both at the server and in new emerging opportunities at the desktop."
The deal is not only significant in terms of the possible beginnings of supplier consolidation to grab a share of this potentially lucrative market, but also in terms of the close ties both companies have with Microsoft.
Microsoft has been a heavy backer and code contributor to Citrix, while XenSource signed a deal with Microsoft in July last year enabling Windows Server virtualisation to run Xen-based operating systems.
The interoperability deal paves the way for the para-virtualisation of Windows with the Xen hypervisor, granting XenSource exclusive access to the upcoming Microsoft Viridian hypervisor code.
Viridian will be key to those waiting to upgrade to Windows Server 2008, and that plan to use the update to Windows Virtual Server 2005 and the latest server release to serve as hosts for virtual machines running earlier Windows versions.
But this latest version of Windows Server is not due out until early next year. And Microsoft has said it will defer key features in the final Viridian hypervisor code to meet a release date that will be a full 180 days after the new server product is released.
These delayed features are the live migration of running virtual machines between server boxes and the addition of hardware resources like memory. The maximum number of virtual processor cores has also been reduced from 64 (as with XenSource and VMware) to 16.
Another virtualisation supplier is SWsoft, which offers its Virtuozzo operating system-level server virtualisation software for creating virtual private servers to run on one physical server.
Although the software can run multiple Linux or Windows virtual private servers on a server, it is not possible to run multiple virtual private servers based on a mix of Linux and Windows on the same server.
SWsoft chairman and chief executive, Serguei Beloussov, said licensing was now becoming a limiting factor in a market that made it difficult for the plans of enterprise IT managers to work within varied and complex compliance arrangements.
"It has a lot to do with changing business models," said Beloussov. "There is no technological problem to move environments across boxes, it is just the licensing that holds some companies back. We have regular discussions with Microsoft, for instance, and advise our users to report any relevant environment changes," he said.
"But as CPUs get faster and memory becomes cheaper, virtualisation will be usable in wider aspects of IT enterprises, and perhaps make the monopoly suppliers look again at licensing."
Pursuing open source
By contrast, VMware has pursued its avowed open source philosophy in trying to promote the interoperability of its products through key building blocks of the IT infrastructure stack. In April 2006 it made the virtual machine disc format specification for managing the running and storage of virtual machine environments. It said more than 2,000 suppliers and developers have since requested to review and use the format.
And the possibility of embedding VMware's hypervisor into the server hardware of OEMs may not be so far-fetched a way to counter growing threats to its dominance as virtualisation moves mainstream. It would have the effect of getting VMware certified by more independent software suppliers at the same time.
Indeed, XenSource has followed a similar course in support of its open source credentials - despite its Microsoft ties - by making its Xen software freely available. And competitors, such as Virtual Iron, have built commercial product sets aimed at enterprises based on the Xen hypervisor.
All of which moves the market towards a viable virtual desktop infrastructure for enabling virtual machines to run multiple PC client instances instead of server ones.
Virtual desktop infrastructure encapsulates the server, storage, software and network virtualisation activity of a busy and growing market as its logical endgame.
This delivers applications that can be dynamically run and managed at desktop level, with cost-effective personalisation, access, security and back-up across an entire enterprise.