So the latest version of the Windows 10 tech preview is out and it is pretty snazzy! Being the daredevil rouge that I am I decided to try it out on my work laptop (being the only Windows PC I have) and have had great success. While I wanted to try it out I didn’t want to chance destroying all my data and I also wanted an easy back out if I didn’t like it. Neither a format/reinstall nor an upgrade suit these requirements so it was time to try something even cooler, booting from VHDX!

Most people will know VHD(X)s as the file format of Hyper-V but there is another cool way of using this disk image. Windows (or really the boot loader) has had the feature of booting from VHD since Windows Vista but it hasn’t been a really popular one. This is a shame as it is a great way to test out different Windows versions without much risk.

There are two main ways of installing to VHD(X), doing a normal Windows install via USB key/DVD or using DISM to apply the install WIM directly to the VHD. The only real difference between the two options is the Windows boot loader will be upgraded with the “normal” install and be graphical. The DISM way will give you just the usual text boot loader. I did the “normal” way but the choice is yours.

Without further ado, the steps.

What you will need

  • Windows 10 Technical Preview ISO from
  • If you are following the “normal” way:
  • USB key for booting
  • Windows USB/DVD Download Tool from

Setting up the Windows 10 disk

First we will need to setup the virtual hard drive that Windows 10 is going to live in. No matter which “way” you choose you will need to perform these steps.

  1. Open command prompt
  2. Type diskmgmt
  3. Go to Action then Create VHD
  4. In the Location: box type C:\Win10.vhdx
  5. We want to use the newest VHD format available so select VHDX if it is available to you
  6. As I don’t want to waste all my disk space in one hit I selected Dynamically expanding (Recommended)

Note: Dynamically expanding only says recommended when you use the VHDX format however you can use it with VHD. The only small downside to dynamically expanding is a performance hit as there will be more than one operation per write. 7. I selected a Virtual hard disk size: of 40GB as I won’t be installing that much and I will still have access to my original operating system as an E: drive 8. Click OK 9. Once the disk is created you will see an uninitialized disk ready for Windows 10!

The Normal Way

  1. Insert your USB key and find out which drive letter it is
  2. Install the Windows USB/DVD Download Tool that was downloaded earlier

Note: You will need .NET 2.0 to install this tool. 3. Launch the tool and follow the wizard to copy the ISO to the USB key 4. Reboot the computer and boot from the USB key 5. Follow the wizard as per every other Windows install until you get to the disk configuration section 6. Press SHIFT+F10 to launch a command prompt 7. From the command prompt we will now attach the VHD(X) using the following commands

diskpart select vdisk file=E:\Win10.vhdx attach vdisk 8. Click back to the disk selection screen and then click refresh 9. You should now see your blank drive 10. Select the drive and click next

Note: You will see a message that it can’t be installed on this drive, you can safely ignore that. 11. Finish the Windows install 12. On next boot you will be prompted to select which operating system to boot, just select Windows Technical Preview to get into your new Windows 10 install!

The DISM Way

  1. Right-click the new drive and click initialise
  2. Format the drive as NTFS
  3. Mount the drive as letter X:
  4. Find your Windows 10 ISO (it should be something like Windows10_TechnicalPreview_x64_EN-US_9926.iso)
  5. Double-click the ISO to mount it (or use your favorite ISO mounting tool)
  6. Check the drive letters of the new VHD(X) and of the mounted ISO
  7. Assuming the mounted VHD(X) is X: and the DVD is mounted as D:, run the following command to apply the Windows install

dism /apply-image /imagefile:D:\sources\install.wim /index:1 /ApplyDir:X:\ 8. Once DISM is complete the new drive will need to be added to the boot menu with the following command

bcdboot X:\Windows 9. Now the computer can be rebooted 10. On next boot you will be prompted to select which operating system to boot, just select Windows Technical Preview 11. Windows 10 will now finish installing to get ready for first use

Going back

Don’t like Windows 10 or are having issues?

  1. Reboot to get into your previous operating system by selecting it from the boot loader
  2. Backup the BCD store using BCDEdit

bcdedit /export c:\bcd_store_backup 3. View the BCD store to grab the identifier of Windows 10

bcdedit /v 4. Delete the Windows 10 entry

bcdedit /delete <identifier string> 5. Delete the C:\Win10.vhdx file from your hard drive