Preparing for Windows 9 with dualboot

As most of you know, Microsoft will announce Windows 9 om September 30th 2014 which is in 2 weeks as I write this. Now I am very excited about this product and considering there hasn’t been any information about the new features yet I predict a lot of testing when the technical preview (really Microsoft, just call it a beta) is released to the public.

So how do we test this new operating system?

The initial thought is to use a hypervisor, like Hyper-V, and create VM’s with Win9 on, but imo that really isn’t a very good way to try the client OS. Therefore I wanted to share my approach which is to initially install Windows 9 on a VHDX file and set it in a dualboot configuration with my Windows 8.1 system which I’m currently using. Unless I find something that tells me otherwise, Windows 9 will shortly be my main OS. There are 2 big advantages to running this in a VHDX with dualboot instead of a vm:

  1. You get a much more true test how the OS will run on your hardware since it actually reaches your physical hardware with the exception of hard drive which is virtual. I find this particularly important when testing a client OS.
  2. You can by all means and purposes replace you current installation but it is still very easy to fall back to should something occur, or if you just have to get some files that you haven’t backed up or put into the cloud

So now that I have convinced you all on why this is a good idea I will show you how to easily do it. In the procedure below I’m using Windows 8.1 to mimic the Windows 9 iso since it’s not available until 2 weeks from now.

There are 3 stages for getting a VHDX file in dualboot with your existing 8.1 installation:

  1. Create a vhdx file
  2. Apply the new Windows image to the vhdx file
  3. Set up the boot configuration


Create the vhdx file.

Here I create a dynamically expanding 40GB vhdx file on the folder c:\boot on my C:\ drive.

Create the folder to store the vhdx file, C:\boot in this example

open an elevated commandprompt and type the following

create vdisk file=c:\boot\win9.vhdx type=expandable maximum=40960
attach vdisk
list disk

Verify that the VHD is selected by the star on the left

create partition primary
format fs=ntfs quick

Now the vhdx fine has a formatted and active partition, in this case it was mounted as E:


Apply the new Windows image to the vhdx file

Now that the vhdx file is ready, you mount up your newly downloaded Windows 9 iso, in this case it’s mounted as D:

First you have to pick the SKU you want from the iso. Note the name and Index#  from this command (Again Windows 8.1 is used in this example)

dism /get-imageinfo /imagefile=d:\sources\install.wim


Now I see I can either install Windows 8.1 or 8.1 Pro. Since I want 8.1 Pro so I must apply Index 1 to my vhdx

dism /apply-image /imagefile=d:\sources\install.wim /index:1 /applydir:e:\

Wait for the operation to complete


Set up the boot configuration

The vhdx file is ready but not set up as a boot option on your computer so we still work in the elevated commandprompt.
Add the vhdx to the boot menu

bcdboot e:\windows

To check you boot configuration

bcdedit /enum

The boot configuration

Notice that the description is the same which makes it confusing but the device tells us which is the vhdx-file. Also the vhdx file is the default boot option.

If you want your current installation as default boot then simply run

bcdedit /default {current}

And last I want to change the desciption to tell them apart, which hopefully won’t be necessary with the genuine Windows 9 iso.

bcdedit /set {b42c4225-3dc5-11e4-94b6-c190548f218f} description “Windows 9”

After you run bcdedit /enum again you should see something like this


Finally we are ready to test this, simply reboot your computer and you should see the new and improved boot menu in Windows 8.1

The boot menu

Make sure you check out “Change defaults or choose other options”, lots of neat stuff there.

Final words: Yes, I am perfectly aware of all the tools that can do this for you, but you won’t improve you skills in diskpart, dism og bcdedit by using those tools. The best way to improve in something is to work with it.