With the recent initial public offering of VMware Inc. being greeted with a resounding cheer from investors, it's clear that virtualization is increasingly important to businesses. Corporations are working virtualization strategies into their budgets and plans, and suppliers have responded with a number of products. In fact, two major players in the industry, VMware and Microsoft Corp., are offering their previously for-pay server products for free, presumably to foster demand for their more-expensive and more-capable enterprise systems.

For casual use, of course, the desktop versions of these products -- also freely available -- will work, but what if you want to scale and consolidate multiple physical servers onto one? What if you're interested in management features, monitoring and the ability to move machines from one virtual machine server to another? It's time to consider a server-level product.

Let's take a look at the free server offerings from VMware and Microsoft. In particular, we'll look at the comparative advantages of each -- after all, they both run virtual machines, and they both do it pretty well; it's the features "on the margin" that will make a difference to you.

VMware Server

VMware Server runs on standard 32-bit hardware, although it supports guest machines that are running 64-bit editions of popular operating systems such as Windows, Solaris and Linux. You can do virtual multiprocessing using VMware's Virtual Symmetric Multiprocessing (SMP) feature, and you can also capture the state of any particular virtual machine and subsequently roll it back at any time. This is useful for testing new features of software or for building baseline test environments.

VMware server also imports Microsoft virtual machine format files, and it can import images created with Symantec Corp.'s LiveState Recovery, making it a multifaceted product that's not "siloed" into one proprietary format. The ability to import Microsoft files is a pretty big deal, especially in companies acquiring other companies or in deployments where both products are in use.

You can purchase VMware Server support separately. Since the product is free, there is not any enterprise-class support offered by default. It also does not include any centralized management capabilities; instead, that feature is reserved for the for-pay VirtualCenter software that VMware also sells.

Perhaps the most useful ability in VMware Server is the Virtual Appliance Marketplace. These virtual appliances range from demonstration versions of products that software manufacturers have already preconfigured to fully operable open-source environments. The appeal of these "appliances" is that they're ready to go -- you simply download the appliance file from the Marketplace, open the VMware Server console and the appliance file, and press the virtual power button.

Presto, there's a machine ready to go. It's an excellent way to test alternative operating systems, evaluate new products and even deploy a mini-infrastructure. I'm familiar with several outfits that have used a Linux-based mail scrubbing appliance downloaded from the Marketplace as their first line of defense against spam.

Download VMware Server here.

Microsoft Virtual Server 2005 R2

Virtual Server 2005 R2 used to be a product users would pay for, but it's now available gratis. As you might expect, it bakes in several features that are tied to Windows Server. For instance: support for Volume Shadow Services (VSS).

VSS is a component from Windows Server 2003 where the operating system takes "snapshots" of folders, files and disks at certain times throughout the day. VSS within Virtual Server will allow all a host's virtual machines to be backed up simultaneously. Recovery from an error is equally simple -- select a snapshot, restore it, and the process is complete. No lengthy backups, no shutting down the machine to get around locked files and so on. It's quick and convenient.

You also get Active Directory integration, making Virtual Server a better choice if you're administering and using an AD environment. Virtual Server can publish its binding information in AD as a service connection point object. This makes it easy to see any Virtual Server services residing within a given forest.

In addition, the file-based disks of virtual machines, known as virtual hard drives (VHD), can now be mounted outside of the Virtual Server environment as regular disks, enabling files and folders to be copied to and from the virtual disks. This makes it much simpler to deploy scripts and run malware scans and archive files on virtual machines than it was with previous versions of the product.

Finally, while not as expansive and inclusive as VMware's Virtual Appliance Marketplace, Microsoft has undertaken an effort to produce VHD files with preconfigured versions of most of its server software. While you won't get much client software from this program, you can test products such as Windows Server 2008 Beta 3, Exchange Server 2007 and ISA Server, which can be useful if you rely on Microsoft products to run your network.

Download Microsoft Virtual Server 2005 R2 here.

The last word

Both VMware Server and Virtual Server 2005 R2 are capable products, and the price is right for each of them. They run virtual machines well, and they're each fairly intuitive to use. The differences lie in the subtleties: With VMware Server, you get a broader and more expansive ecosystem for trial virtual machines, while Microsoft's Virtual Server 2005 R2 affords you better integration with your existing IT investment if you're in an Active Directory environment. VMware doesn't play in the Microsoft infrastructure that deeply.

Read the original article on ComputerWorld, here.