Let’s say your primary computer is running Windows 7 and you would also like to install Windows 8 on the same computer but while keeping the old Windows 7 installation intact. What are the options?
You can either run Windows 8 as a VM but for the best experience, you should consider installing Windows 8 on a separate partition of your computer’s hard disk. The advantage is that you don’t have to fiddle with your existing Windows installation and you can easily switch between Windows 8 and your existing Windows version with a press of the restart button. In technical terms, such an arrangement is also known as dual boot setup.
The requirements are simple – your computer’s hard-drive should have at least 30 GB of free space that you can convert into a Windows 8 partition and second, though we aren’t touching your existing Windows partition, it is always a good idea to backup important files should anything go wrong in the process.

How to Install Windows 8 on another Partition

To get started, we first need to create a physical partition on our hard disk. Search for “Disk Management” in the Windows Search box and choose the program with the description – “Create and format hard disk partitions.”
While the Disk Management console is open, select the Drive Volume that you want to partition (C: in our case) and choose “Shrink Volume.”
Shrink Windows Volume
Next you need to specify the size of your new Windows 8 partition. For a basic installation, 30-40 GB should be fine – you need to put this number (1 GB = 1024 MB) in the box that says “Enter the amount of space to shrink in MB.”
Windows will now create a new “unallocated” volume with a similar capacity of 20 GB. Right click that volume and choose “New Simple Volume.”
Disk Volume Size
Inside the Simple Volume Wizard, leave the volume size at the default value, assign a new Drive Letter to this volume and format the partition using NTFS format. That’s it – the new hard disk partition is now ready to house your copy of Windows 8.

Install Windows 8 in Dual-Boot Mode

Let’s now install Windows 8 on the new partition. Insert the bootable Windows 8 DVD and reboot the machine.
If your computer does not boot from the DVD, press F2 (or F12 or  the Delete key) while the machine is booting up to open the BIOS settings. Switch to the Boot menu in BIOS settings and set CD-ROM as the first device in the boot order.
Save the settings, exit the BIOS and your computer should automatically reboot. It will display a prompt – “Press any key to boot from CD or DVD..” and the boot process will pause for a few seconds. Press any key now and it should take you straight into the Windows 8 installer. Just follow the step-by-step wizard to install Windows 8 on the new partition.
Windows will restart a couple of times – you may want to eject the DVD to avoid those “boot from DVD” prompts” – and the installation should be complete in about 15 minutes. Also, it will offer you a “Choose OS” screen so you can change your default OS or switch to another one with a click. The whole thing is pretty user-friendly.