Virtualisation is often seen as complementary to cloud computing but not a necessity.

Dan Kusnetzky, lead analyst of the Kusnetzky Group, said virtualisation is “one of a number of useful technologies for cloud computing”.

“Not all applications of cloud computing require the use of the use of virtual machine technology. They may, however, use virtual access, application virtualisation and/or storage virtualisation," he added.

Cloud computing is more of a buzzword to Subbaraman Iyer, vice president of i2m Management Services, a project-management firm.

"I see that there's very little connection between cloud computing and virtualisation, though they have common underlying drivers," Iyer said.

"Generically speaking, the term 'cloud computing' is just an alternate solution that doesn't use the in-house data centre or any vendor specific hosting resource. It is a virtual huge infrastructure where both computing and storage resource is available on a pay-as-you-go on-demand basis. The compelling benefit is in its scalability and the ability to access an application anywhere."

Web strategies and Internet services consultant Errett Cord, on the other hand, said the two approaches complement each other.

Virtualisation allows user companies to reduce the number of servers being used; cloud computing and virtualisation are two parts of the same effort to create a network setup that's both efficient in its use of resources and redundant in its failover and disaster-recovery preparedness.

Middleware companies, such as Boomi and CohesiveFT will significantly bridge the gap of corporate software applications to the cloud by building virtualised systems that run from cloud computing platforms.

Walt Disney business analyst Steven Algieri called virtualisation "the biggest single reason the cloud gives you scalability”.

"Most of the services you need to scale quickly [in a server environment] are the client-facing services," he said. "A common example would be a web server. If the web server is running a database driven content management system [where] all the actual data is in a large database on a separate server, then having a static configuration of the front-end web server makes it trivial to spin up new instances. All that's needed is a simple script inside to obtain a few custom details [such as the] IP address and database address.”

"This is how Amazon EC2 works," Algieri said. "You create a virtual machine image, and Amazon will then happily spin of as many instances off as you need. Using a service like RightScale then gives the ability to manage these instances.

If the cloud behaves more like an operating-system platform-providing the primary interface through which customers access their applications, virtualisation is clearly a key part of the equation and a tremendous benefit within the cloud, according to Charles Kinnan, a software architect and founder of Milyli, a new company working on rich Internet applications for product lifecycle management.

"[But] it doesn't seem like this is the way that clients for the cloud are moving," he said. "With the variety of devices, screen sizes and input methods 'they' are touting for the cloud, chances are better that client software will still run on the devices and be tailored for each device with the data being sent up and down to the cloud.

"So many new web-friendly, client side platforms are becoming popular - Adobe Flex and Silverlight for PCs, Android for phones - it would seem to me that most cloud computing will rely on client software connected to data storage services."

Within the datacentre, trying to manage a single OS connected to a single user would be a nightmare. “So a good degree or automated provisioning of virtual servers would make a lot of sense," Kinnan said.

In short, he sees cloud computing server farms becoming 'plug and play datacentres'.

In the long term, there is little consensus of how the uber-trends toward virtualisation and cloud computing will mesh, and how smoothly. Still, while virtualisation isn't absolutely necessary for cloud computing, it certainly will help.