This is a set of scripts and configurations to succesfully install and boot Windows 7 and 10 from GPT-partitioned drive on a system with BIOS. This may be convenient if you benefit from GPT features such as partition labeling, unique GUIDs and raised partition count/size limits.

Windows does not permit this by default, the solution is to create a small MBR-partitioned virtual drive and place boot-related files to it, so that Windows will treat this virtual drive as real boot drive and perform all the boot configuration there. The drive then gets attached automatically at every boot so all boot-related configuration tasks which are run after installation (BCD specialization step, updates etc.) complete succesfully.

Setup can be accomplished in the following way:

1. Partition your hard drive with GPT using any external tool available. For example, using GNU parted this may be like the following:

(parted) mklabel gpt
(parted) mkpart primary 0% 10MB
(parted) mkpart primary ext4 10MB 210MB
(parted) mkpart primary ntfs 210MB 100%
(parted) set 1 bios_grub on

This will create small 10MB primary partition at the very beginning with flag necessary to install GRUB into GPT drive, and also 200MB ext4 partition where GRUB root directory will reside.

Also here we create third NTFS partition for Windows which spans to the end of the drive (change this for your needs).

2. Format and mount your GRUB root partition.

3. Install GRUB to your hard drive using grub-install and partition formatted in the previous step as boot directory.

4. Install grub.cfg and MEMDISK from SysLinux into boot directory.

5. You need Windows PE bootable image with ImageX installed into it (does not come by default) and Windows setup DVD. Boot your computer to Windows PE to get access to PE command prompt.

6. Format third partition of your hard drive, for example using DiskPart (assuming disk #0 is your hard drive):

DISKPART> select disk 0
DISKPART> select partition 3
DISKPART> format label="Windows 7" quick
DISKPART> assign letter=c

7. Install Windows using ImageX (be careful with the letter of your CD/DVD here, this assumes D: is your Windows setup DVD):

X:\> imagex /apply D:\sources\install.wim 1 c:

8. Copy boot/ directory from this repository to C:\boot (for example using Samba share).

9. Execute C:\boot\create.cmd. This will create VHD drive and place all necessary boot files in it.

10. The next step is crucial for the whole setup. You should reboot your machine into new Windows installation and mount the boot VHD drive manually before Windows starts to specialize BCD which is located on the VHD. To do this, wait until "Windows is installing devices" message appears and then press Shift+F10 to get command prompt window. Then type this:

> C:\boot\mount.cmd

This may take some time as the script waits until the drive actually appears as a volume, and keeps trying to assign it for 10 minutes. You can check if everything went right by reading C:\boot\mount.log after installation (and after every boot).

If you get this message: "Windows Setup could not configure Windows to run on this computer's hardware", then probably you did this too late and you need to repeat the procedure from step 5.

This has to be done only once during setup. Later we will configure a service to mount boot volume automatically at startup.

11. If setup process continues without errors then all went OK and now we need to configure the system to mount VHD drive at startup in order to allow it correctly handle BCD during updates. You may do this by installing Windows Resource Kit Tools (reg files in this repository assume that Windows Server 2003 Resource Kit Tools are installed). After you install this, you may simply add bootmgr.reg to the registry. This will install the service named bootmgr via srvany.exe utility from the Resource Kit. You can then check if this works by starting this service and looking if the volume B: appears. If all is OK and B: shows in the Explorer you can check if BCD utilities work correctly by e.g. executing bcdedit without args in elevated command prompt and looking for output (it should dump current configuration and not give errors such as "store could not be opened"). If all is OK you can reboot now and see if the service succesfully mounts the boot volume at system startup.

12. Optionally you may wish to hide drive B: from the Explorer window as there is little benefit from it there. Simply merge hide.reg into the registry and reboot (probably relogin will be sufficient).

Once in a while Windows installs updates that, presumably, need to modlfy data on a boot partition. These updates go through reboot and run at early stages of system boot, where VHD mount service is not activated yet. As a result, such updates may fail to install.

You may temporarily move boot partition from a VHD inside of Windows machine to separate physical (or virtual, in case where Windows runs inside a VM) drive, proceed with update installation, and then move boot drive back to VHD inside Windows. Follow there steps:

1. Stop and disable bootmgr service, this can be done from command line with administrative privileges:

> sc stop bootmgr
> sc config bootmgr start= disabled

2. Unmount boot VHD:

> C:\boot\unmount.cmd

3. Copy C:\boot\bootmgr.vhd file to some other machine.
4. Convert bootmgr.vhd from VHD to RAW format, this can be done with qemu-img convert:

$ qemu-img convert -f vpc -O raw bootmgr.vhd bootmgr.raw

5. Write bootmgr.raw to separate physical or virtual disk and attach this disk to Windows machine (either VM or physical).
6. Shutdown Windows machine and make a backup.
7. Attach the disk obtained from step 5 to Windows machine and boot from it. You should see boot drive as a separate physical disk in a running Windows (use Disk Management utility since the drive may be hidden), and updates should install normally.
8. After installing updates, re-create boot VHD by executing

> C:\boot\create.cmd

9. Enable bootmgr service back:

> sc config bootmgr start= auto

10. Shutdown Windows machine, detach physical or virtual boot disk and start it back from primary drive.

1. Big thanks to wzyboy and his original post about boot from VHD drive on reboot.pro (in English: http://reboot.pro/topic/19516-hack-bootmgr-to-boot-windows-in-bios-to-gpt/page-2#entry184489) which gives the base idea of booting Windows from VHD with GRUB. 90% of this code was written using his instructions.
2. SysLinux MEMDISK is described here: http://www.syslinux.org/wiki/index.php/MEMDISK
3. Microsoft's article on creating a User-Defined Service: https://support.microsoft.com/en-us/kb/137890
4. An article about building Custom Windows PE Image: https://technet.microsoft.com/en-us/library/cc709665(v=ws.10).aspx
5. GNU Parted: http://www.gnu.org/software/parted/
6. GNU GRUB: https://www.gnu.org/software/grub/