VHD or Virtual Hard Disk is a hard disk (virtual) that contains an operating system that resides in a folder in your computer or add-on storage device.
storage device.
This example will show you how to create Windows 8 VHD file using Windows 7 Diskpart Tool:
To Create a Windows 8 VHD:
1) Open the command prompt in Administrator mode (right click and run as administrator)
2) Type
diskpart and hit enter
3) tye
create vdisk file=c:Win8.vhdx maximum=20480 type=expandable, this creates 20GB VHD file in C drive
4) Type
select vdisk file=c:win8.vhdx to work on the created VHD file
5) Type
attach vdisk, ignore an alerts that would ask you to format the disk
6) Type
Create partition primary
9) Type
Assign letter G:, choose any available drive letter for your VHD drive
10) Type
format quick label=Win8-VHDX, after this step, you should have G drive show up on your computer drive list
11) tYPE
exit to exit to the command prompt
12) type
dism /apply-image /imagefile:E:sourcesinstall.wim /index:1 /ApplyDir:G:, note: replace the E: with your
Windows 8 location and replace G: with your VHDx drive creaed in step 9
13) Go back to DiskPart by typing
diskpart in the command prompt
14) Type
select vdisk file=c:win8.vhdx
15) Type
detach vdisk to unmount the virutal drive from your system

That is set, your VHDX file that contains Windows 8 is created and ready to be deploy to any computer. See the instructions
bellow to modify the boot options of your computer using the BCDEdit (Boot Configuration Data) .
1) Open the command prompt in Administrator mode (right click and run as administrator)
2) Backup computer boot configruation before make any changes by typing this command
bcdedit /export c:Backup-Boot-Config - this will create backkup of your boot configuration
3) Edit the existing boot store by typing
bcdedit /copy {current} /d "Windows 8 Native VHD", this will create new boot
entry by copying the existing entry
4) Copy the boot identifier created above includeing the braces {....} and type
bcdedit /set {....} device vhd=
[c:]win8.vhdx, replace {...} with your boot idnetifier.
5) Type
bcdedit /set {....} osdevice vhd=[c:]win8.vhdx, repace {...} with your boot identifier.
6) Reboot the computer and you should boot option to boot to Windows 8 VHD in addition of your regular operating system
Command Prompt result from the above BCDEdit instruction
C:Windowssystem32>bcdedit /export c:backup-boot-config
The operation completed successfully.
C:Windowssystem32>bcdedit /copy {current} /d "Windows 8 Native VHD"
The entry was successfully copied to {61c685ad-b3e1-11e4-b86b-b77e16e0a215}.
C:Windowssystem32>bcdedit /set {61c685ad-b3e1-11e4-b86b-b77e16e0a215} device v
hd=[c:]win8.vhdx
The operation completed successfully.
C:Windowssystem32>bcdedit /set {61c685ad-b3e1-11e4-b86b-b77e16e0a215} osdevice
vhd=[c:]win8.vhdx
The operation completed successfully.
C:Windowssystem32>