Hardware & Infrastructure
Commentary
3/30/2004
05:23 PM
Fred Langa
Fred Langa
Commentary
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Langa Letter: Virtual Excellence: Microsoft's 'Virtual PC' Is Too Good Not To Check Out

In this introduction to the technology, Fred Langa says Microsoft Virtual PC provides a viable alternative to dual booting and should be a solid choice for software testing, evaluation, and support.

Many Benefits
Obviously, a VPC is a wonderful testing tool because any operating system, application, or utility crashes that occur in the VPC will be safely contained and won't affect the main operating system. You can even reboot the VPC and watch it go through what appears to be a complete "hardware" shutdown and restart while you continue to use the real, physical PC and its main operating system, uninterrupted.

But the VPC also offers other benefits. For example, take ease of backup and recovery. Each VPC sees its own, separate hard drive, which behaves in almost every way as an utterly standard hard drive, even to the point of being able to be FDISKed, partitioned and formatted. But in reality, the "hard drive" is just a single file on the host operating system's real hard drive. That file is managed by the VPC software (running on the host operating system) which can grow and shrink the virtual hard drive file as needed. The VPC software also uses a form of compression to keep the file small. On my system, for example, a virtual drive that appears to be 18 Gbytes to the virtualized operating system is a single file on the host hard drive that actually occupies only about 1.25 Gbytes of real disk space.

Because each virtual hard drive resides in what is really just a file, backing up a virtual hard drive is simply a matter of copying that single file. For example, once a virtual PC is set up perfectly, just the way you want, you can shut it down and use your normal file tools to copy the virtual hard drive's file to a safe location or medium. Later, if the virtual PC gets fouled up beyond repair (through testing, user error, hacking, whatever) you can just copy back the stored hard drive file, and the virtual PC will instantly be restored to the way it was when you saved its perfect setup.

Suspend, "State Save," And More
When a VPC session is running, you can pause it at any point: When paused, the VPC session then gets no CPU cycles and remains frozen in time until it's un-paused. If you wish, you can even completely exit the VPC session; the Virtual PC Console will ask if you want to "save state" or simply exit. If you choose the former, the virtual hard drive is frozen, and the entire memory contents of the virtual PC session are saved to the host disk. This means you can restore the VPC session in the future to the exact point--even to the exact clock cycle--at which it was suspended.

This can be a huge time saver because you can restore a saved session far faster than a reboot. In fact, on my system, it takes only about 10 seconds to fully recover a saved VPC session!

This is wonderfully handy. For example, if you just need to check something out quickly in another operating system, instead of rebooting to a dual-boot setup or starting a second physical PC, a VPC lets you access a saved session in literally seconds. You can find your answer, and re-save the VCP (also just a few seconds) and you're done--all with essentially zero interruption of your normal operating system, which stays open and running the whole while.

Screen One

Screen One
(click image for larger view)

Enormous Power
Again, it can be easier to see what all this means than to read about it in the abstract, so let me demonstrate with screen shots captured from my personal PC:

Screen One is a capture of my standard XP Pro desktop; the Microsoft Virtual PC console is running. Several previous VPC sessions have been saved, but none are active at the moment.

Let's start with something simple: We'll restore a DOS session, shown in Screen Two.


Screen Two

Screen Two
(click image for larger view)
Note that this is not a "DOS window" or "Command window." Rather I've booted DOS on a full, independent, virtualized PC running inside XP. To give DOS something to do, I've run an ancient (1987!) version of the old "Microsoft System Diagnostics" to show some of the specs of the virtual PC; we'll come back to these specs later.

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