About two weeks ago, I purchased the latest version of VMWare Workstation, v6. I've been using both VMWare and Microsoft Virtual PC now for probably about 5 years on or off.

There are two good reasons that I've found to use virtualization software: To test installations & setups, or to test in alternative configurations such as different operating systems or operating systems with different configurations.

I've recently found a third reason though: To run application software that I do not want to install on my primary O/S. For example: Our ERP system uses Crystal Reports v9, which is an older version of Crystal Reports. I've recently purchased Crystal Reports v11, which is not entirely backward computable and which automatically upgrades any older versions of Crystal it finds when installed. So that I can use Crystal v11 with some new web applications I'm working on, I set up a development environment in a VMWare virtual machine. When I need to develop with Crystal v11, I start up the virtual machine and maximize it. It's easy to forget that I'm working in a virtual environment.

VMWare instances are reasonably portable as well, so I've been able to put my virtual machine on a USB hard drive and take it home, where I can run it using the free VMWare player software. This is much more convenient than taking my entire laptop home.

Microsoft Virtual PC is free, however the VMWare snapshot feature that lets you save a configuration and quickly return to that configuration at any time is more than worth the $190 cost of VMWare.

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A few days ago the most recent copy of Information Week magazine arrived, and the front page story was how VMWare is going to supplant Microsoft. VMWare's key advantage? That they have a hypervisor and Microsoft does not (currently). Essentially, a hypervisor is a very compact O/S that allows multiple operating systems to more efficiently run on a single server.

I've set up Microsoft's Virtual Server before, just to evaluate it, and found it somewhat more sluggish when running the same apps than either VMWare workstation or Virtual PC. It does have a significant advantage in that it does appear to be a real server on the network and it runs as a service so when the hardware reboots the virtual machine is there. I assume that VMWare's server product has similar capabilities.

There are definite advantages to using virtualization software to host multiple virtual servers on a single physical server. I can think of a few:

• Ease of backup and restore. Setting up and configuring a server and the applications that run on it can take days. If the installation is done on a virtual machine, then the entire machine can be easily backed up and restored. The host physical server need run only the virtual machine software. Moreover, the virtual machine can be restored to a different physical server, so hardware failure becomes easy to accommodate.
  
  
• Security. Enterprise services can multiply like rabbits, with each server having unique access permission requirements. When using physical servers, there's a strong cost incentive to colocate as many services on a single server as possible, rather than buy, then support, new hardware. With virtual servers, the HR software can have its own virtual server and since it doesn't need IIS, IIS doesn't need to be installed on the virtual server. However, the HR virtual server can run right along side the market forecasting software which does require IIS. Both servers are supported by different vendors and each vendor can be granted access only to the virtual server that is running their product.
  
  
• Testing. Rolling out service packs and upgrades to enterprise applications can be a nightmare task. With virtualization technology, it need not be. Just make a copy of the HR server. Apply the service pack to the copy. Verify that everything is working correctly then replace the production virtual machine with the upgraded copy. What could be easier?

There are a few gotchas though, and here are two:

• Performance is the most obvious. A virtual server will always run more slowly than the bare hardware. I think hypervisor technology may ameliorate this problem somewhat but it's always a concern that will need to be addressed. You may want to think twice, for example, before putting your data warehouse SQL Server on a virtual machine.
  
  
• The other issue, Support, is not so obvious. How do you keep all your servers up with the most recent patches and service packs? Microsoft makes this easy, with Windows Update and when running a Microsoft OS a virtual machine is no more difficult to administer than a physical one. As the InformationWeek article points out, however, if folks start writing applications than run directly on top of the VMWare software, then this could become a bigger issue.
  
  Let's say that one vendor configures Java and Apache to run directly on top of a VMWare environment. Another vendor does the same thing but in a slightly different way. Now, when an urgent security threat must be patched, IT administrative staff must update vendor 1's server in a different way than vendor 2. It's a step back, perhaps many steps back to the days before we had update managers such as windows update or the java machine's automatic update.

I just thought of another good use for virtualization technology: Updating a user's PC can be a time consuming task for the help desk. Users often have lots of software installed that has to be reinstalled on the new PC, data must be copied over and mapped drives and network connections reconfigured. What if each user were given a virtual machine that runs on their PC. When upgrade time comes along, the virtual machine is moved from the old hardware to the new hardware. Quick and easy!

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To sum it all up, virtualization is cool and, InformationWeek aside, represents no immediate threat to Microsoft's domination of the operating system market.