Computer virtualisation is a method of emulation that's used by many organisations & individuals. It allows computer users to create "virtual computers" inside an actual computer. The reason computer virtualisation is so useful is because: computer users can install any operating system inside a virtual computer without having to restart the real computer (or having to manipulate the real computer's hard drive in any way). As a result, computer software can be stored & executed inside the virtual computer without any incompatibility issues.
Another advantage to virtualisation is that computer viruses caught on a virtual computer cannot spread to the real computer. This is because the virtual computer is a series of files (each representing a hard drive, motherboard, etc.) that are not accessible to a real computer without virtual software. The virtual computer is, essentially, a sand box where no sand can escape; no software/files/changes can escape the virtual computer & spread to the actual computer. Best of all, recovering from viruses in a virtual computer is only a matter of overwriting the infected "computer" with a back-up.
There are many virtualisation programs sold on the market; VMWare Workstation, Parallels Workstation, Virtuozzo, Simics & ICore Computer 3-in-1 are a few examples. But there are several that are free (including Microsoft Virtual PC, which can be downloaded here or in the Downloads page).
The first thing to do is install Virtual PC (or which ever virtualisation program is being used). Install the program with all the desired virtualisation drivers for the actual computer (such as network bridge drivers). Once that is finish, a virtual computer can be created; simply click on the Start button & locate the shortcut for Virtual PC.
After starting Virtual PC for the first time, a virtual computer wizard will appear. Click on the Next button, select the radio button labelled "Create a new virtual machine," give the virtual machine a name, save it in any directory on the actual computer & hit the Next button. Then, select the desired operating system to install from the drop-down menu (the menu will only contain Microsoft operating systems, but others can be installed in the virtual machine by selecting Others from the menu). For a good list of operating systems that do & do not work in a Virtual PC-based virtual machine, go to the following website:
After selecting an operating system, select the radio button labelled "Adjusting the RAM" & hit the Next button. Adjust the RAM so that the virtual computer can run without causing any problems to the actual computer (i.e.: do not use all of the RAM because the actual computer may crash). Then, hit the Next button & create a virtual hard drive; give the virtual drive a name, select the check box labelled "Enable undo disk" & hit the Next button. Save the virtual hard drive in any directory on the actual computer & adjust the size of the virtual drive (the maximum size of the virtual hard drive must be a bit less than the total amount of free space on the actual computer's hard drive). Hit the Next button & hit the Finish button.
Now that a virtual machine has been created, installing an operating system is a simple matter of having an actual installation disk at hand or having a disk image of the installation disk. If the operating system requires a license key, a registration number or a serial number, make sure that it is also at hand. To install the operating system from an actual installation disk, insert the installation disk (be it an optical disk or the first of a set of floppy disks) into the actual computer's drive. Then, select the newly created virtual machine in Virtual PC, select Start & open the Media menu at the top of the window. From there, it is a simple matter of selecting either the Mount Host CD/DVD Drive option or the Mount Host floppy Drive option. Then, follow all installation instructions that appear on the screen. If floppy disk images or optical disk images are to be used, select either the Load ISO Image option or the Load Floppy Disk Image option instead.
When the installation of the operating system from actual media is complete, simply eject whatever disks are inserted in the actual computer's drives. When the installation of the operating system from a disk image is complete, open the Media menu at the top of the window & either select the eject floppy Media option or the Eject CD/DVD Media option to release the disk images. If an operating system is being installed from a set of floppy disk images, remember to eject the first image & load the next image when prompted do insert the next disk.
Lastly, run the virtual machine again & log into the newly installed operating system. Note that computer peripheral use & file access between the virtual & actual computers is very limited at the moment. If any version of Microsoft Windows is installed inside the virtual computer, in order to use the virtual machine more efficiently, open the Media menu at the top of the window & select the Install Current VM Additions option. This will execute an installation file inside the virtual computer; simply proceed with the installation. The virtual computer will restart & communication to/from the actual & virtual computers will be seamless. Sadly, this option is not available when using any variant of MS-DOS or when using any Linux distribution; this will only work if a Windows environment is installed inside the virtual machine.
Now, the virtual machine can be used for anything, from evaluating software to running legacy applications that would normally be incompatible with the actual computer.