I've been a big fan of virtual pc products like VMWare and Virtual PC for a long time. I actually first used Virtual PC on a Mac. As a long time user of VMWare, I gave up when I had too many problems with version 4 and couldn't get tech support to respond (but that's another story) and switched to Virtual PC.
Since I do a ton of testing on pre-release products, I find using virtual PCs a great tool. One of my favorite features is Undo drives. Basically, you do a bunch of work for a while and then when you shut down the virtual PC, you can just throw away the changes or keep them and have the changes merged with your main image. Well, yesterday I got a great tip from a co-worker, Ken Getz [0].
You see, I've got a two 9 Gb virtual PC images (assigned 512Mb of RAM) with VS 2003, SQL 2000 SP3, Whidbey, and Yukon that I'm using for my pre-con on Sunday. One runs Windows XP, the other Windows 2003. Ken got tip from a mutual friend, Bernard Wong (the former wizard behind the agent [1]). It seems Virtual PC has a feature called Diff Drives.
Here's what you do:
- Create your Virtual PC as normal. Install your software and get it ready for use.
- From the main Virtual PC File menu select Virtual Disk Wizard. Hit next on the first wizard page.
- Select Create a new floppy or hard disk image and click next.
- Select Create a hard disk image and click next.
- For the disk location, specify a file name for the DIFF drive. One way to do it is to navigate to your current virtual PC's VHD file, select it and then add Diff_ as prefix.
- Once you've got a file name, click next.
- Now select the third option on the list Differencing Disk Image and click next.
- On the next page, select your main Virtual PC VHD file and click next. This is called the parent drive.
- Finally, click Finish.
At this point you need to make one adjustment to your existing virtual PC's settings. You need to change your hard drive to point to the DIFF VHD file, not the main. Once this is complete, you can now use your virtual PC and not have your huge multi-gigabyte file be touched! In fact, you can even mark your main image read-only.
What I love about this is that I can use my VPC all week and at the show and not have to worry about always undoing. Once I give the pre-con, I can throw out my DIFF drive and I'll have clean virtual PC to work with on other testing. How sweet it that? One more thing, you can continue to use an UNDO drive with your DIFF drive. This brings up one more benefit: merging changes from your UNDO drive to your DIFF drive is so much faster in my subjective tests. Enjoy!
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