Dual-Boot Mac OS X Snow Leopard and Lion

Apple recently released the first preview of Mac OS X Lion, the next generation Mac operating system scheduled for release this summer. As with all new operating systems, most techies are keen give it a try, but being a preview build you would be crazy to attempt to use it as your primary operating system. 

The best option is to dual-boot Lion alongside a fully supported version of Mac OS X, such as Snow Leopard. This is exactly what I've done and it gives you the best of both worlds, allowing you to test Lion, but as soon as you come across something that doesn't work correctly (and you will), you can jump straight back to the safety of Snow Leopard.

This article will explain how to partition your hard drive for the Lion installation, without impacting your existing operating system. However, as with any low level system changes, please ensure you have completed a full backup before proceeding.

1. Go to "Applications > Utilities > Disk Utility".

2. Select your hard drive from the left pane and "Partition" from the right pane.

3. Click "Volume Scheme" and select "2 Partitions".

4. You can now set the size of your new partition, which will be used by Mac OS X Lion. I suggest a minimum of 20GB, but if possible push for 35GB, which will give you enough space to test your applications. Also you should name the partition, for example "Mac OS X Lion". When your are ready click "Apply".

5. Once your hard drive has been partitioned you are now ready to install Mac OS X Lion. This can be done by launching the installation file (DMG) that was downloaded from the Mac App Store. When prompted, select your newly created partition and your Mac will automatically restart and install Mac OS X Lion.

6. When the installation is complete you can switch between operating systems by restarting and holding option key during boot-up (just like with Boot Camp). You can also select your default operating system by loading "System Preferences > Startup Disk" and highlighting the partition you would like to load by default.

You now have the best of both worlds, enjoy!