Easier Dual Boot for 8 & 10

Discussion in 'Windows 10' started by jhoff80, Oct 3, 2014.

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  1. jhoff80

    jhoff80 Pen Pro - Senior Member Senior Member

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    I posted this as a response in a Surface based thread, but really it's more general information so it probably belongs here too. If you want to try out Windows 10 dual-boot and are concerned about mucking with partitions, you don't have to be. Windows 8 and 10 can both boot from a virtual hard disk (VHD) file. It's basically a file on your main partition that the bootloader sees as a separate hard disk.

    So first thing is to back up your boot configuration (see note at the bottom for more)... so in your working install of Windows 8, run the following:

    BCDEDIT /export c:\bcdbackup.bak

    Then, make sure that your hard drive has a lot of free space (in my example I used 80GB).

    Boot your USB key, and then press Shift-F10 to open command prompt.

    Then you'll want to run something along these lines (note that the drive letter might not be C after booting from the USB drive, you'll have to figure that out in the command prompt on your own):

    diskpart
    create vdisk file=C:\Win10.vhd type=expandable maximum=80000
    select vdisk file=C:\Win10.vhd
    attach vdisk

    You can then close out of the command prompt, and after going through setup and selecting the "Custom" button, you'll see your ~80GB (or whatever size you did) drive as unallocated space on a separate disk. Choose to install to that. Then you're completely finished. Windows 8 (and 10) boot natively from a virtual hard disk file.

    If you ever want to get rid of Windows 10, you can boot into Windows 8 from the menu that'll pop up each boot, and then delete the VHD file.

    This was sort of originally based on Scott Hanselman's article for the Windows 8 preview, but I've been doing it ever since:
    http://www.hanselman.com/blog/Guide...s8DeveloperPreviewOffAVHDVirtualHardDisk.aspx

    NOTE: In a later article I hadn't yet seen, he makes a good point that users probably should backup their bcd file (this is what configures which OS boots up).

    http://www.hanselman.com/blog/HowTo...ws8ConsumerPreviewOffAVHDVirtualHardDisk.aspx
     
  2. dblkk

    dblkk Pen Pal - Newbie

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  3. jhoff80

    jhoff80 Pen Pro - Senior Member Senior Member

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    VHD is true dual-boot, and doesn't involve messing with your hard drive partitioning. There's absolutely zero reason to repartition your drive.
     
  4. jhoff80

    jhoff80 Pen Pro - Senior Member Senior Member

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    ...And of course, I have to take that response back. Apparently the updater in the technical preview just doesn't work with a VHD install at this time. :mad: :oops:
     
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