How to install Windows 8 alongside your normal OS

Windows 8 is ready for download, but it's not yet ready for the bigtime. As our preview revealed, Microsoft's next operating system is fast, responsive and stable already, but with the developer still describing it as 'pre-beta', you shouldn't be using it as your primary operating system just yet.

That's a problem, as the free-to-download installer overwrites your existing installation -- albeit without touching your accounts and files -- and the only way to get back to Windows 7 or earlier is to reinstall from the original media.

If that's putting you off trying it out and seeing what all the buzz is about, help is at hand in the shape of VirtualBox. This free download for Windows, Mac OS X, Solaris and Linux creates a virtual computer on your hard drive, sharing resources with your core system so you can install alternative operating systems, including Linux and Windows 8, inside your existing OS.

This is also a neat solution for Mac users who need to run an occasional Windows application, and thus can't justify the expense of a physical PC.

Install VirtualBox

1. Virtualbox will install on pretty much any recent Intel or AMD processor. It needs 30MB of disk space for its own codebase, and we'd recommend a further 60GB of space for each virtual machine you want to install, as this has to accommodate not only the OS system files but also any applications you want to run within it, plus your data, settings and media.

You'll also need to give over some of your system memory to the guest OS, with Windows 8 demanding at least 1GB for the 32-bit install and 2GB for the 64-bit version. This will be deducted from your system memory, and won't be available to your regular host operating system all the time the guest OS is running.

2. Download the version of VirtualBox appropriate to your operating system from virtualbox.org and run through the regular installation routine. You don't need to choose at this point how much space you want to give to your guest operating system, so just choose a destination and click through the dialogues.

Don't worry if you see a warning that you'll be disconnected from your local network: as soon as the installation has completed your connections will be re-established.

Install Windows 8

3. The Windows 8 installer is a free download. Microsoft provides it as a .iso image file. To install this from a DVD in the regular manner you'd need to burn it to a disc, first expanding the image to extract the files it contains.

This won't be necessary once Windows 8 goes mainstream, as it can read .iso images natively, presenting them as a live media resource in Windows Explorer.

You can skip that step when installing a virtual machine, as VirtualBox sees the .iso image as an installer, extracting the necessary files to set up the guest OS.

Point your browser at msdn.microsoft.com/en-us/windows/apps/br229516 and download the file marked Windows Developer Preview English, 32-bit (x86). It's a 2.8GB image; save it to your desktop so that it's easy to find when you come to use it.

4. Now launch VirtualBox and click New to create a new virtual machine. Give it a logical name - we've called ours Windows 8 - and choose Windows 7 as type of operating system you want to install. You can choose Other Windows if you like, but we have found the Windows 7 setting to work well.

Set the amount of memory devoted to the virtual machine to at least 1GB, remembering that this amount will be unavailable to the rest of your system while you're running Windows 8, so aim to strike a balance between your native and guest operating systems.

5. You now need to clear some space on your hard drive to store the combined operating system, its applications and your files. Select to create a virtual disk and if you don't plan on using any other virtualisation software with your installed guest operating system choose VDI (VirtualBox Disk Image) as the disk type.

6. Choose whether the disk space should be dynamically allocated or set at a fixed size. Fixed is best if you can afford the space as it's faster, but for those with smaller hard drives or less free space it might be too extravagant, as some of the allocated space will be sitting empty. If that applies to you, choose to have the space dynamically allocated, in which case the virtual machine will grow as and when needed -- but never actually shrink when you remove content.

VirtualBox will suggest setting your disk to 20GB, which is fine if you're using dynamically allocated space, but if you're using a fixed amount, increase this to around 60GB to give your OS room to grow in the future. Your virtual machine will now be created. You just need to install an operating system onto it.

7. Click Start on the VirtualBox Manager toolbar to launch the First Run Wizard, and point it towards your downloaded .iso image file. You'll be asked to confirm that it's correct by clicking the Finish button. There isn't one; it actually means click Start.

VirtualBox will now boot Windows in a new window and run you through the regular setup routine. Follow the on-screen instructions, selecting the appropriate language settings and supplying a computer name, username and password. You don't need to supply a serial number with this pre-beta release, but you will need to activate it over the Internet.

If you have an active net connection throughout the set-up, the installer will take care of this for you. If not, make the Control Panel (linked from the Metro tiles) your first stop, where you'll find the activate option at the very top of the list.