The benefits of server virtualisation are reasonably well understood in the enterprise, enabling firms to make optimal use of hardware resources, move workloads around and, if necessary, implement a failover policy that will let another system seamlessly step in and take over operations if a physical server should stop working.

On the client side, virtualisation has so far only seen sporadic adoption and is not so well understood. Nevertheless, vendors such as HP are now turning to client virtualisation as a way of providing enterprise customers with benefits such as increased data security, availability of applications and data almost anywhere, and a simpler way of managing end-user accounts.

HP recently unveiled its own vision of client-side virtualisation at a summit in London, and the company’s broad definition of the term encompasses a number of different technologies, including server-based computing, blade PCs and workstations, plus virtual desktop machines.

“HP views virtualisation as being about separating where the applications are run from the location where the user is accessing them,” explained Andrew Gee, sales manager of remote client solutions at HP.

A similar view is taken by Citrix, which has recently overhauled its software line-up to enable users to connect to a traditional server-hosted Citrix session, a virtual machine or a physical blade PC. However, Gee claimed that HP is the only enterprise vendor capable of providing a complete end-to-end solution covering everything from servers and infrastructure to client access devices, and also the software thanks to its partnerships with Citrix and VMware.

Many of the technologies outlined above have been available for some time from a number of different suppliers, but HP appears to be promoting itself as a single source that can let enterprise customers mix and match any or all of these differing methods of supporting workers as needed.

“What is the best solution for each customer? We’ve always said that there isn’t one size that fits all,” said Gee. To be successful, any overall solution needs to be scalable and manageable for users, he added. “If you end up with something worse than your users’ existing environment, then it will not be a success,” Gee said.

HP’s concept revolves around giving different users access to different resources, depending on their login profile. There are four basic profiles, according to the firm, starting with task-oriented workers who can be supported with a Citrix session or web-based enterprise applications running on HP servers.

A step up the scale are users who need to operate at least a couple of basic productivity applications, and these might be supported by virtual desktop infrastructure (VDI) technology consisting of a pool of virtual client machines that also live on a server farm in the datacentre.

Meanwhile, knowledge workers will typically require their own dedicated PC, according to HP, and this can be provided in a centralised manner by using blade PCs that sit in a rack-mounted enclosure.

HP’s blade PCs have been available in Europe since early 2007 and can cut management costs by 50 per cent over four years compared with standard desktops, according to the firm. Each blade is comparable to an entry-level PC with an AMD Athlon 64 chip and up to 4GB memory.

The most demanding users, such as design engineers and stock market traders, need access to a workstation-class system. HP can also offer this in a blade format, but this time its current hardware is based on dual-core and quad-core Intel processors with up to 16GB of memory per blade.

Key to the whole scenario is that the same access device can be provided in each case, according to HP. “With a thin client, the desktop piece is identical across all these usage cases. You can log in and get access to the right resources from anywhere,” said Gee.

This kind of architecture, where data and applications are hosted centrally and worker access is via an appliance-like desktop client, is reminiscent of the minicomputer and mainframe-based data processing departments of the past.

Although this has the benefit of greater security for data and makes for easier management, it also has its disadvantages. Thin clients have been around for at least a decade, but they have been perceived as offering a poorer user experience than a desktop PC.

Phil Dawson, agenda manager for virtualisation at analyst Gartner, said that things are now changing, and it is not just HP that is promoting this computing model. “What has changed is that bandwidth is a lot better, which means you get a much better user experience,” he added.

Dawson said he believed that enterprises will increasingly deploy more of this kind of infrastructure in the future, but was cautious about it displacing standard PCs as the mainstay of corporate computing anytime soon.

“If it grows to even five or 10 per cent [of user desktops], it will be a very big displacement of PC deployments,” he said.

One issue that firms need to be conscious of is the danger of savings made on the desktop translating into higher costs elsewhere. “If you centralise some of these assets, suddenly they become a central cost. You could find you’re just moving the cost from the desktop to the datacentre budget,” said Dawson.

Gee said that he believed most enterprises would eventually converge on this kind of centralised solution over time, but that some markets may be faster to adopt it than others. “A customer has to have a specific issue they are trying to solve. They won’t do it if we just turn up and say it’s a good idea,” he explained.

The motivation for moving to this kind of virtualisation will depend on which market a potential customer is in. For financial firms, security and availability of resources is key, he said, while management is less of an issue. For retail outlets, management is often the most pressing concern, while insurance firms need flexibility because they often acquire rivals and need to merge their IT operations quickly.

Finance firms are the keenest early adopters because of compliance concerns, according to Gee, but there are new issues that are driving uptake of client virtualisation as well.

“Customers are looking to put disaster recovery plans in place, so that they can continue to work if staff can’t reach their premises, and there’s also energy consumption ­ - some finance firms simply can’t get any more power into their building in the City, but they still need to bring in more staff,” said Gee. In the latter case, client virtualisation enables most of the power-hungry systems to be moved to a datacentre located elsewhere.

One criticism of client virtualisation is that it does not sit well with another trend in enterprise IT ­ - mobility. At least half of all PCs now sold in Europe are laptops, and forcing the users of these to connect to a server-hosted session is seldom likely to be feasible. For this reason alone, PCs are unlikely to give way to thin clients in the foreseeable future.

However, one way of reconciling virtual clients with mobility is to let travelling workers take a virtual machine with them. VMware announced plans at its European VMworld conference in February for what it calls Offline Virtual Desktop Infrastructure, whereby users can “check out” a virtual machine from the server onto their laptop for use offline and then check it back in when they return to the office.

“At Gartner, we class a virtual machine that is a client as a ‘bubble’ precisely because it can move. It can be server-based, or it can be moved to offer a secure environment on another client,” said Dawson.