There are two methods to dual boot Chrome OS. The first allows you to install Chrome OS without touching any previous OS you may use but requires two HDDs/SSDs.
The second method allows you to install Chrome OS and another OS on the same HDD/SSD but will require you to format that drive losing any current OS you have.
Method 2 is experimental and not guaranteed to work.
- Remove all HDDs/SSDs apart from the one you wish to install Chrome OS on.
- Install Chrome OS following the usual instructions.
- Once done, reconnect your other drives and use the boot menu to change your boot preference.
- If you wish to be given a boot option on every boot you will need to use a boot manager for this, if not simply use your Motherboard boot options to select which to boot on boot.
- Install Chrome OS on the HDD/SSD you want to have multiple OSs on. THIS WILL FORMAT YOUR DRIVE! If you have more than one drive, remove them first.
- Once Chrome OS has installed, use a GRUB live CD or any other partition manager than can manage STATE partitions to partition the STATE partition into a partition type your other OS can read.
- Boot your OS installation media and when asked where to install your OS, pick the empty partition that you have just made.
- Install your OS.
- Once this has completed you will need to use GRUB again to set up a boot manager and select the Chrome OS BOOT partition and the Windows boot partition as your boot options.
- When your turn your computer on, you will then be given an option of what OS to boot!