Want to install dual boot OS (Windows 8 & Ubuntu 16.04) on external 2TB Seagate HDD with Non-UEFI (BIOS only supported) by running either Windows 7 OS or Ubuntu 16.04 installed from 4GB USB drive.


Make either 4GB USB drive or Seagate HDD as a bootable disk for all installed OS.

What I have:

  • Host machine (Running Windows 7 Ultimate - 32bit - BIOS)
  • Seagate external HDD - 2TB (GPT - The Drive, to be install both Windows 8 - 64Bit & Ubuntu 16.04 - 64Bit)
  • Sandisk USB drive - 4GB
  • Sony USB Drive - 8GB



  • Seagate 2TB HDD already has some separate NTFS Partition and formatted using a GPT partition table, want to install OS on that separate partition on the same disk.
  • System does not support UEFI (BIOS only)
  • System supports boot from USB stick/external HDD

  1. (Host Machine - Windows 7 - BIOS Mode)

    • Installed Windows 8 files using "WAIK" (Without boot loader/manager)
    • Then installed Ubuntu on the 4GB USB drive (Using Unetbootin)
    • Then restarted, and booted from the USB drive and tried to install Ubuntu on another partition on the Seagate drive.
    • Then restarted again, but it doesn't detect the bootloader from Seagate disk, instead directly boots to host machine


If we try by installing "windows boot manager" on another 200MB, FAT32 USB drive, then is the host machine must running on the UEFI supported machine..? or is the host machine being in BIOS enough?

  1. (4GB USB Stick - Ubuntu 16.04 - Try Mode)

    • Opened "Gparted" tools
    • Formatted another "Sony 8GB Pendrive" as, (FAT32, 200MB Partition)
    • Install Ubuntu from the same running Ubuntu, except set the Bootloader location as "Sony 8GB" FAT32 partition (No error occurred)
    • Restarted, set "Sony Drive" as the first boot drive, but it doesn't detect the boot loader from Sony Disk, instead directly loads to host machine

Please note: * Want only in GPT partition table (No idea how to convert back to BIOS)

Any idea is much appreciated, thanks in advance!

  • did you put grub bios partition on the GPT disk? BIOS can only boot from MBR disks. thus the Grub Bios partition is needed to supply the required boot structure
    – ravery
    Aug 28 '17 at 7:00
  • PS: to revert to BIOS disks, just repartition them as MBR
    – ravery
    Aug 28 '17 at 7:08
  • @ravery Thanks. Ok, let's i consider the option for revert to BIOS disk as a final solution. Before of that would like to check any other option will works.
    – Jai K
    Sep 17 '17 at 9:29

If I understand correctly, you want to end up with a 2TB external USB hard disk that uses a GUID Partition Table (GPT) and that includes BIOS-mode installations of both Windows 8 and Ubuntu. Unfortunately, this is impossible -- or at best, it's so bleeding-edge that you might as well forget about it. The problem is that Windows will boot in BIOS mode only from Master Boot Record (MBR) disks, not from GPT disks. There are a couple of bleeding-edge ways around this limitation, like this approach (which I've never tried) or using Clover, but getting either of these things set up is unlikely to be worth the effort.

Instead, I recommend you drop your GPT requirement. Even if the disk contains data you want to preserve, you can do a lossless GPT-to-MBR conversion with gdisk, as described in my gdisk documentation here. This will produce an MBR disk that you should be able to make bootable.

Another issue you must understand is that most OSes, including both Windows and Ubuntu, have installers that try to install boot loaders for the same boot mode in which the installer booted. It sounds like you're trying to use a second computer to do the OS installation, so it's imperative that you boot the OS installers in BIOS mode if you want the resulting disk to be bootable in that mode. This may require enabling the BIOS/CSM/legacy support in the firmware setup utility, and you'll need either luck or enough knowledge to take control of the boot process to force a BIOS-mode boot. See this page of mine for more on this topic. Note that details of how to force a BIOS-mode vs. an EFI-mode boot vary from one computer to another.

Finally, Windows tends to be fussy about its hardware, so installing on one computer when you intend to use it on another may not work; or at best, you're likely to need to reboot multiple times to massage the driver configuration. It's likely to be simpler to install using the ultimate target computer. Also, my understanding is that Windows won't install to external hard disks. There may be hacks to work around this limitation, but I know nothing about them. You may need to ask on a Windows forum to get advice on these issues.

  • Thanks for pointing out this link. It seems to be good.
    – Jai K
    Sep 17 '17 at 10:13
  • [Install Windows 8 to External USB HDD] (** Worked **) This link is more useful.Just check it out.
    – Jai K
    Sep 17 '17 at 10:18

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