If you need to run more than one operating system on a single PC there are several ways to do it. You can have separate hard drives for each OS, and connect only the one you need. Or, you can dual-boot two or more operating systems on the same hard drive, with each version of Windows or Linux - say - in its own partition. Here, though, we'll show you how to install another operating system in a virtual machine so you can boot it up on your Windows desktop whenever you need it. No need to reboot, have multiple hard drives or separate partitions. Plus, it's free!

It's called virtualisation and involves creating a software model of a PC’s hardware. With this model in place you can install and run a so-called 'guest' OS in that software PC or, as it's more commonly referred to, a virtual PC.

The guest OS is totally independent from the host OS although you can readily swap between the two and some virtualisation software allows you to exchange files between the guest and host.

One thing a virtualisation package doesn’t model in software is the processor which means that the guest operating system must use the same processor as the host operating system. In the world of PCs this means versions of Windows and Linux variants. In theory it also includes Mac OS but, because of licensing issues, it generally isn’t possible to run this operating system under Windows via virtualisation. (You can run Windows on a Mac, though, using Boot Camp.)

How to install Windows 8 on a Virtual PC

Here, we’ve installed the evaluation version of Windows 8 (the latest 8.1 Enterprise is available from Microsoft's website) onto a virtual PC. You may not want to do that, but the same principles apply when install any OS you like as a virtual machine.

We’re using the free Oracle VM VirtualBox so, before continuing, download it from www.virtualbox.org and install it on your PC.

1. Start VM VirtualBox. As the introductory text explains, the lefthand part of the window is initially blank because this is where your virtual computers will be listed but you haven’t created any yet. Click on the New icon and the ‘Create Virtual Machine’ dialog box will appear. Enter the name of your new virtual machine and you’ll notice that Type and Version update accordingly. Click the image below to enlarge


2. Click Next and the next dialog box will ask how much memory to allocate to the virtual machine and you should accept the default by clicking on Next.

VirtualBox memory

3. Next you’ll be given various options for your virtual machine’s hard drive you want and, again, we suggest that you accept the default value, this time by clicking Create.

VirtualBox hard drive

4. Now you’ll be asked what file format to use to define your virtual machine. Accept the default of VDI by clicking Next.

VirtualBox hard drive

5. Your next option is whether to allow the virtual hard drive to grow as it is used and, yet again, we suggest accepting the default so click on Next.

VirtualBox hard drive

6. Enter a name for the virtual hard drive. Click on Create to accept the default of a 25GB hard drive.

VirtualBox file location

7. Your virtual machine will now be created and this will be reflected by the fact that your chosen name of ‘Windows 8’ appears in the left pane of the main window and details are shown to the right. You’ll notice that that your Windows 8 virtual machine is shown as Powered Off so start it up by clicking on the Start icon (the green arrow above). Click the image below to enlarge

VirtualBox main window

8. A second window appears – this is the screen of your virtual machine. If any information or error boxes also appears just click on OK. Since your virtual machine has no operating system installed, a dialog box now appears asking what it should boot from. We’ll be booting from the disk image of the Windows 8 trial. Click the image below to enlarge

VirtualBox start virtual machine

9. Click on the folder icon to the right of ‘Host Drive E:’, navigate to the Windows 8 trial file you downloaded, select it and click on Open. Now, back on the ‘Select start-up disk’ dialog box, click on Start. Various error and/or information messages may appear but in most cases you can just accept them.

10. The Windows 8 installation will start and you should follow the prompts as you would with any other Windows installation. So, on the first page, for example, select ‘English (United Kingdom)’ as the Time and currency format and ‘United Kingdom’ as the Keyboard or input method language.

VirtualBox install Windows 8

11. During the installation you’ll be asked whether to do an Upgrade or Custom installation. Because your virtual machine had no previous version of Windows installed on it, only the Custom option is applicable. Soon after this, the message ‘Installing Windows’ appears. Now would be a good time to put the kettle on.

VirtualBox install Windows 8

12. Eventually, having gone through the whole installation procedure, the familiar Windows 8 start screen will appear, allowing you to try out the latest version of Windows and use it exactly as if it were a physical computer.

VirtualBox Windows 8 installed and running

13. When you’re done, just select Close from VM VirtualBox’s Machine menu. This will close your virtual machine, just like a real machine running Windows 8, which means that all your settings and files will be saved for next time you start up this virtual machine.