A Virtual computer looks like a window on the desktop of your normal computer with another operating system running inside. For example you can run Windows XP and have a window on you desktop that has a copy of Windows 98 running on it.

Virtual computing is not to be confused with Dual Booting. Dual Booting is where you have two or more separate operating systems installed on your hard drive. With Dual Booting you can only run one operating system at a time. Virtual computing allows you to run more than one operating system at the same time.

On the desktop, virtual computers look very similar to remote desktop sharing, but obviously that's where the similarity ends.

Before we get started, i recommend you examine the image at left for a better understanding of how the Virtual computer looks when running on your computer  (click for a larger image).

Being able to access a second or third operating system has a whole heap of uses and i've seen quite a few imaginative solutions, but it's especially helpful for;

Program Developers
You can install more than one OS on your development computer. This lets you test your programs and code on virtually any operating system known to man! No longer will you have to go and dig out that old Windows 98 PC in the garage to test your software. We recommend setting up a PC in the corner of your lab with all the common operating systems installed as virtual computers. This way you can easily test your software without slowing down your development computers -  a must for any software development house.

University Students
If you're studying another operating system or a program that will only run on another operating system you can use a Virtual Computer to save you the headache and potential loss of data that can occur when setting up Dual-boot configurations. One good example is Oracle. Most students find that their notebooks or desktop PCs are running XP, but Oracle requires Windows NT/2000/2003 Server. VMWare let the students simulate the Server environment without having to upset their previous XP installation.

Lab Demonstrators
You can install an entire network using virtual computers. you could set up, for instance a Windows 2003 server farm with a number of servers and workstations. Students could benefit from setting up networks and solving configuration problems. I have heard of one lab demonstrator who ran a virtual farm of 50 computers - obviously there are some serious resource requirements when you get to these sorts of numbers.

Network Administrators
You can test out new software, drivers or even windows patches on a virtual computer before you deploy it to your network - this could save you hours of reinstallation if you find a bug that won't work with your setup. If a server goes down on your network you could fire-up a virtual computer that would occupy the same addresses etc as that server in an attempt to provide some fail-over capacity for your network users.

Security Professionals.
You can set up multiple honey-pots that are whole operating systems complete with dummy data for your network. If you do have an intrusion, you can study what the intruders do and how they do it. This can provide valuable information about hackers skill levels as well as obfuscating your real network computers from the hackers. If you provide particularly tasty false information on these virtual PCs you may even be able to track where your information goes.

Practical Jokers
Scare your workmates! install a virtual computer on their PC with windows 95 or 3.11 (if you have it). If you maximise the virtual computer operating system to be full screen it will look like the PC has reverted to a darker time. When they finish crying you can show them their original operating system is un-touched. :-)

Anyway, lets get with the lingo. The operating system you already have installed on your PC is known as the Host operating system, the operating you install under or inside the host operating system is known as the Guest or Client operating system.

Virtual computers seem pretty reliable. The trick that makes virtual computer emulation so cool is the concept of simulating the hardware of the PC rather than modifying the guest operating system to make it work within the Host operating system parameters.

When you create a new Virtual computer you can even see the Guest PC booting up in the window - complete with a pretend BIOS and Energy-Star! If you look at the device manager of the guest operating system you will notice that the hardware listed is not the same hardware that you have in your PC. This is because the Virtual Computer software is simulating the hardware and has chosen fairly generic devices for compatibility. Devices such as Gigabit network cards may be listed when infact you only have a 100mbit network card. Obviously any network transactions between the host and the guest pc don't actually get routed over the network card so the speeds can peak well above the maximum speeds for your network card.

Most Virtual computer software will let you pause the guest operating system, so you can quickly start and stop the virtual PC without having to wait for the guest operating system to boot up - it's just like a virtual hibernate mode. I've even seen students copy their virtual computer onto a cdrom or memory stick, take it to university and then fire it up on one of the university computers. This is fantastic because you can carry around a whole computer environment - complete with programs and data and all you need is a computer to access it - great for travelling light.

Hardware requirements for running a Virtual computer can be taxing. If your host PC has only 256mb of RAM and you wish to install a copy of windows Server 2003 (which has a minimum memory requirement of 128mb) you will find that 50% of your memory gets consumed by the guest PC. This leaves only 128mb left for your Host PC  - so you will want to make sure you have plenty of spare RAM before running a virtual computer

The two virtual computer programs we reviewed had an optional small piece of software that could be installed on the Guest operating system. This software smooths the transition of the mouse cursor from the Host to the Guest environment. Both products made this installation a one-click experience that it definitely recommended.

One good idea we came up with was to run Windows 2003 in a virtual computer and install Microsoft WSUS on the guest operating system.

Microsoft's WSUS Server is a junior version of Windows Update for you network. Simply point all your PCs at the IP number for your virtual WSUS server and then you can fire up your WSUS server only when you need it. 

The image at right shows such an installation in a paused state, notice the list of 'hardware' and the networking selection. The screenshot (within the image) shows the last state of the virtual computer. If you unpause this server it will resume from this point (click for a larger image)

Virtual PC
Microsoft
Virtual PC 2004 Trial Edition

Microsoft's Virtual PC 2004 only works on host PCs running Windows 2000, XP(sp1+) and Windows 2003. There is a great trial version available from Microsoft that you can test out to see if it will be suitable for your requirements.

The process of setting up Virtual PC couldn't be easier. Just install the software, create a new Virtual Computer, put in your cdrom of the Guest Operating system and away you go. Once you're up an running with your new operating system Microsoft's Virtual PC interface is probably easier to use than VMWare.

One thing that we found with Microsoft's Virtual PC 2004 trial was that the networking facilities weren't quite up to scratch. You can connect to the internet or the host computer from the Guest PC (proxied through the host operating system running NAT), but you are unable to connect to the guest PC from the host PC or any other PC on the network. This means that Virtual PC is almost useless if you want to run network services such as the Windows Systems Update Server (WSUS) or any applications that bind incoming ports such as databases, file and mail servers etc..

VMWare Workstation
VMWare
Evaluate VMWare Workstation

VMWare workstation is a far more flexible solution for a virtual computer - it works on virtually any operating system including all versions of Windows and most Linux distributions.

One of the key features that makes VMWare Workstation that makes it stand out is it's Bridged mode networking. You can set up your guest operating system so that it has an IP Number and is placed on the network with all of your real computers. This way you can connect directly to the virtual computer across the network just like it was a real computer. VMWare is the natural choice for use in the honey pot or oracle situations mentioned above because the PCs will look and transact like normal network PCs.

If you're having trouble connecting from the guest to the host pc of visa versa, remember that because VMWare is fully network aware, you'll need to check to see that you have appropriate firewall settings.

VMware have been developing their virtual computer software much longer that Microsoft. They're definitely top dog in the industry so its going to be pretty tough for Microsoft to shake up the VMWare crowd.

We'd definitely recommend VMWare if you need to connect to the guest computer from a remote networked computer.

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