Being able to carry your PC’s entire operating system, data and applications around on something as small as a USB flash drive, mobile phone or MP3 player isn’t a particularly new idea.

Some Linux distributions are designed for this purpose, and tools like BartPE let you create cut-down versions of Windows XP that can run from a CD or USB stick (see our feature on this topic here).

And technologies like U3 offer specially modified versions of applications for use on portable storage devices.

But now there’s a new generation of applications that use virtualisation technologies to take this idea even further and ­ in many cases ­ free you from the chore of buying modified applications or operating systems.

Some of these products let you quickly create fully featured pocketable PCs, while others can virtualise individual applications, allowing you to carry around your favourite working environment on a keyring and run it on any PC, without leaving any traces behind.

In this feature we’re going to look at some of these free and low-cost applications and what you can do with them, plus we’ll look at the basics of how virtualisation works.

And finally we’ve a practical step-by-step workshop that shows you how to create your own free, portable Linux PC on a USB stick using the Moka5 virtual machine application.

What is virtualisation?
Virtualisation is something that’s quite hard to get your head around if you’ve never encountered it before. The concept has been around since the 1960s in the world of mainframe computing, but in the past few years has started to trickle down to the humble desktop PC.

Put simply, it’s a method of emulating or simulating hardware using software. This allows a ‘host’ computer (the physical PC) to run multiple virtual ‘guest’ computers, each with their own operating system, at the same time.

The original idea was to make the most efficient use of the available computing power of the system, while protecting the underlying hardware from rogue software by using a robust application (known as a hypervisor) to control virtualisation.

What virtualisation can’t do is emulate hardware that doesn’t exist on the real PC ­ so you couldn’t emulate a DVD drive on a PC that only has a CD drive.

Why virtualise?
In a virtual PC environment, the guest operating system or application has no direct access to the real physical hardware on your PC ­ every request to access the hardware goes through the hypervisor.

The guest OS thinks it’s running on a totally isolated PC and has no awareness of anything outside the virtual environment. The emulation extends to a virtual BIOS, graphics card, network card, hard disk, CD-Rom and so on ­ it’s easiest to see this in action in Microsoft’s free Virtual PC 2007, where you see a traditional PC boot-up screen and can even change settings in the virtual BIOS just as in a physical PC.

But one of the main attractions of virtualisation is that it makes security management much easier. Since you can isolate a virtual PC totally from your ‘real’ PC you can, for example, create a virtual PC specifically for web browsing and email, knowing that whatever viruses or spyware you accidentally catch pose no threat to your ‘real’ PC and data.

To get rid of any infections, you can either reset the virtual PC to an original fresh, clean installation ­ a process that can take just a few seconds ­ or delete the entire PC.

Similarly with virtualised applications ­ the idea is that these are ‘sandboxed’ from the operating system and can’t affect any other files or processes on the PC. But in use they look and feel just like an ordinary application. Two rather different examples of this are Ceedo and Bufferzone, which we look at below.