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The Developer's Guide to Building Virtual PCs : Page 4

Walk through a step-by-step Microsoft Virtual PC 2004 installation of SuSE Linux 9.1 Professional. Once it's built, you can clone your Virtual PC, back it up, perform experiments on it, restore it, and even distribute it to others.


Tips I Wish Someone Would've Told Me

The following tips can save you time and aggravation when working with Virtual PCs. Use them to get the most out of your VPC investments.

1. If you are installing a Windows OS in a Virtual PC, you can save yourself at least half an hour by doing a quick format of the virtual hard disk instead of a full format. What you're skipping is the extensive testing that the format utility does to find bad disk sectors. It's not a real disk, so the testing is essentially useless—assuming that you have a reliable physical hard disk on your host computer.

2. When working with Virtual PCs, you have the option to turn on "undo" disks. This option allows you to experiment with a VPC and decide at the end of your session whether to commit your changes to disk or return the disk to its original state. It's not as great as it sounds.

In my experience, undo disks slow the VPC down to a crawl. Instead, you can "clone" a VPC. For example, if you have an existing Windows XP VPC, you can copy its hard disk image file to a new VPC. If the experiments you do with the cloned VPC work, you can make that your new base VPC and delete the original. If the experiments fail, you can delete the clone. If the experiments create a configuration you want to keep in addition to the base configuration, then you can keep both around.

3. Three factors limit the number of VPCs you can keep and run: disk space, RAM, and your time. Disk space is obvious: if a VPC takes between 500 KB and 5 GB of space on your host machine's hard disk, it's easy to chew up disk space by keeping too many VPCs live. Writable DVDs are a good way to store VPCs offline.

The RAM limit is not so obvious. You would think that VPCs could utilize the large virtual memory space of your host PC, but they are limited by the actual RAM in your host. For example, with the 256 MB SuSE VPC you created running, the host PC has only 450 MB of its total 1,024 MB of physical RAM available. With the VPC closed, the host PC has 750 MB of its physical RAM available. In other words, the VPC takes up all the physical RAM you allocated, plus about 45 MB. That makes sense, because emulating the hardware also takes some RAM.

What about your time? Just like a physical PC, a Virtual PC needs not only to be installed but maintained as well. The disk file needs to be backed up. The operating system needs to be patched. The antivirus needs to be kept up to date, and the anti-spyware solution needs to be kept up to date.

On the other hand, if a VPC gets a virus and you have been faithful about backing up the virtual hard disk, restoring to a clean backup is a snap: delete the infected image file and copy the saved disk image back from a DVD in just a few minutes.

4. If you're planning to buy a new PC that will run multiple VPCs, include one or more big hard disks, a big backup, lots of RAM, and the fastest CPU you can get. The computer I use mostly for VPCs has 1 GB of RAM; I often wish it had two. It has a 160 GB hard disk; I often wish it had two of them and that they were even bigger. It has a DVD Writer that has worked out well for backup, but I often wish it also had a USB2 external hard drive.

It's only money, but giving this machine the ability to run multiple VPCs eliminates the need to buy a whole bunch of other computers.

Martin Heller is a Web and Windows programming consultant. He writes from Andover, Massachusetts.
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