The benefits of software virtualisation

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Speak to most IT marketing professionals, and they will try and convince you that virtualisation is a new phenomenon. In truth, the concept of running one program inside another has been around for years.

Ten years ago, Sun popularised the notion of virtualisation with Java. The system's innate portability was due to a virtual machine that created a sandbox for secure applets. IBM has also used a hardware abstraction layer to separate applications from the underlying systems in its enterprise machines.

Today, the concept of virtualisation has evolved. Companies like VMWare and Xen have promoted the notion of running a whole operating system, either on top of another, or atop a hardware-based Hypervisor. However, some companies are now preaching application virtualisation, in which software applications are insulated from the underlying operating system using an insulating layer. The layer protects the application from the registry, causing system alterations to be written to an alternative store, so that the underlying operating system remains unchanged.

Differentiating virtualisation

One of the differences between some of today's application virtualisation systems and the Java virtual machine is that the applications are conventional pre-compiled applications, ostensibly installed on the computer just like any other application and run natively. The JVM, on the other hand, interpreted the code or ran it using a just-in-time compiler, contained in a resident virtual machine.

Why would an IT department want to deploy applications in this way? Lower support and maintenance costs are the obvious answer. "People mostly use imaging tools or [Microsoft's] Systems Management Server to deploy operating system images that include applications," says Scott Reynolds, a consultant at IT consultancy Morse, describing the traditional way of rolling out corporate software. "If that's your mechanism, then every time you have to update an application, it creates additional workload and increases the load on the network."

"An organisation will go through a testing phase where they test all of their applications alongside each other, for conflicts. The largest organisations have more applications, and multiple versions thereof. If you can choose your testing timeframe or even eliminate it entirely, then that is something that application virtualisation will bring you."

It becomes possible with some systems for IT departments to install and uninstall applications more easily, often with a single click, or even for an employee to run an application or server from a USB key on a different machine.

Creating a self-contained software environment

Ideally, virtualised applications will be able to run atop their own insulated software layers without causing conflicts within the operating system. In some instances, different versions of the same application can be run alongside each other (handy if you want to beta test Office 2007 without abandoning Office 2003, for example, or ease the transition from one application to another).

Even Microsoft is now using elements of application virtualisation within the Vista operating system. Under its User Account Control regime, users are encouraged to run programs under standard accounts, to restrict privileges. Many software applications are designed to run in privileged mode, especially for activities like changing the registry. The system uses a virtual registry to enable applications to run in a less privileged mode.

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