I know you know this but I’ll say it anyway: Virtualization is the hottest ticket in the IT biz. But some people don’t understand there are multiple ways to virtualize a computing environment.

Consider Microsoft’s Virtual PC for Mac. This system provides what appears to be an Intel PC platform running on a PowerPC processor under OS X. This type of virtualization is called emulation and relies on emulating an entire hardware environment, processor and all devices, in software. While this works fine it has one significant problem: a huge performance overhead because emulating a processor in software takes a lot of processing power.

Another example of virtualization by emulation is PearPC, which emulates PowerPC hardware on Intel processors.

An alternative to emulation is native virtualization, which creates virtual machines on the core host processor, resulting in less overhead because the processor can execute all instructions at hardware speeds. This is the method used by Microsoft’s Virtual PC, which runs only on Intel processors under Windows.

The introduction of processors from both Intel and AMD that include hardware support for virtualization gives native virtualization a performance boost.

Products that implement native virtualization and can use hardware assistance if it's available include VMware Workstation and Parallels.

As if that isn’t enough, other options include:

* Paravirtualization, which is like native virtualization but requires “guest” operating systems to be modified (for example, XEN now owned by Citrix and VMware ESX.

* Operating system virtualization, which creates virtual machines (also called virtual environments or virtual servers) from the host operating system (such as Virtuozzo.)

* Application virtualization which encapsulates applications (for example, Microsoft Application Virtualization.

I bring all of this up to position the product I want to discuss today: MojoPac from RingCube Technologies. Running with Windows XP only, MojoPac gives you, in effect, a portable Windows XP desktop using operating system virtualization to create an isolated Windows XP guest virtual machine that runs alongside the host Windows XP.

The reason I describe MojoPac as a portable desktop is that it isn’t installed on your PC — it can only be installed on and run from a USB 2.0-interfaced mass storage device, such as a flash drive (nerd stick) or USB-interfaced disk drive. As you might guess, it is better to use a disk-based storage device for performance reasons (an iPod is a good choice as it is fast and something you usually carry around).