I want to make my computer dual bootable. I have installed ubuntu 14.04. I followed tutorials on youtube. I have already made NTFS partition for the same. (image link from Gparted attached)


While installing windows, it says "You cannt install in GPT partition". So it tried to use diskpart in cmd there, to convert it into MBR (read somewhere), but there it was showing only one disk of volume around 930GB (cant remember the exact value but it was of same range), and had a '*' mark on GPT type. So i cant convert it to MBR, bacause i may loose my data, right? How can i make it to MBR ? Or is there any other method to install/ make proper partition?

  • Both Windows & Ubuntu install UEFI or BIOS in the mode you boot the installer. And Windows only installs to gpt with UEFI and only in BIOS to MBR. So if you want UEFI/gpt boot in UEFI to install Windows in UEFI. But Windows likes additional partitions if gpt. BIOS & UEFI Windows partitions, note system has totally different format & meaning between BIOS & UEFI msdn.microsoft.com/en-us/library/windows/hardware/… You can use fixparts or gdisk to convert from/to gpt, but you will need to reinstall grub and make other fixes. – oldfred Sep 18 '16 at 19:44

First, please understand that both the GUID Partition Table (GPT) and the Master Boot Record (MBR) are partition table formats. As such, they apply to the entire disk, not to individual partitions. That is, you can't have one partition in GPT form and another in MBR form. (A partial exception is if you use a hybrid MBR, but those are ugly and dangerous hacks that should be avoided except in certain limited situations, mostly involving Macs that dual boot with older versions of Windows.)

Second, the error message you received indicates that the Windows installation medium was booted in BIOS/CSM/legacy mode; when booted in this way, Windows insists on installing to an MBR disk, rather than to the GPT disk your computer has. The way the message is written makes it sound as if the partition table is the problem, but that's not really the case here -- it's the boot mode of the installation medium that's the problem. Your partition table makes it look as if Ubuntu is probably installed in EFI/UEFI mode. The key point here is that you should not mix boot modes -- if Ubuntu is installed in EFI mode, you should also install Windows in EFI mode. Although it's possible to back up and re-install Ubuntu in BIOS mode (on an MBR disk), or to convert your existing Ubuntu installation to BIOS mode (and to convert the disk from GPT to MBR), that's the hard way to resolve the problem.

The easy way to resolve the problem is to get the Windows installer to boot in EFI mode. There are several ways this may be done; however, no one method is guaranteed to work, because there are several possible reasons it's booting in BIOS mode now:

  • Disable the Compatibility Support Module (CSM) in your firmware. Unfortunately, a lot of Web sites suggest enabling the CSM as a routine part of Ubuntu installation, but that's bad advice, as described on this page of mine. If you disable the CSM on your computer, the Windows installation medium may start booting in EFI mode, and the installation should proceed normally.
  • Re-write the Windows boot medium. Depending on the Windows version, how you obtained the boot image, and how you prepared the boot medium (if the boot image didn't come as a physical medium), you may need to re-write the boot medium. Some tools omit or damage the EFI boot loader when preparing boot media, and some images (especially pirated images or very old versions of Windows) may lack the EFI boot loader entirely. My CSM page covers tools to write images, but from a Linux perspective; some details differ for creating Windows boot media. You might want to ask on a Windows forum if you need more help.
  • Use the computer's built-in boot manager to select the correct boot option. In some cases, the built-in boot manager may show two options to boot from an external medium, with one option including the string "UEFI" and the other lacking that string. Be sure to select the option that includes the "UEFI" string.

Note that Windows added EFI support with Windows 7; earlier versions lack EFI support and can only be installed in BIOS mode. (There are exceptions for exotic platforms.) Thus, if you're trying to set up a dual-boot with, say, Windows XP, you should ignore most of the preceding and convert to a BIOS-mode installation.

Finally, be aware that when you install Windows on an EFI-based computer, Windows will set its own boot loader as the default, and you will then be unable to boot to Ubuntu. There are several ways around this problem, such as:

  • You can use the computer's built-in boot manager in perpetuity -- the same one you use to tell the computer to boot to an external medium. It should present options for both Ubuntu and Windows. On many computers, though, accessing this boot manager is inconvenient, and on some there are bugs or design flaws that make this approach unworkable.
  • In Windows, download the EasyUEFI tool and use it to adjust the boot order; move the ubuntu entry to the top of the boot list. When you reboot, Ubuntu will boot. You'll then need to run sudo update-grub to make GRUB detect Windows. On subsequent boots, you should see both Windows and Ubuntu in the GRUB menu.
  • In Windows, open an Administrator Command Prompt window and type bcdedit /set {bootmgr} path \EFI\ubuntu\shimx64.efi. This does something similar to what EasyUEFI does, but without involving third-party software.
  • Install my rEFInd boot manager. You can do this in Windows (which is a bit tedious); or download the USB flash drive or CD-R version, use it to boot to Ubuntu, and install the Debian package or PPA. rEFInd will take over as the primary boot program and give you the option to boot either Windows or Ubuntu.
  • Run Boot Repair from an Ubuntu emergency disk. This tool will completely re-install GRUB and make it the default boot manager. This approach is overkill and, in rare situations, can make matters worse; but a lot of people are familiar with Boot Repair and so can help if you do run into problems with it.

There are quite a few variants on these options, as well as other more exotic possibilities, such as using any of half a dozen or so other boot loaders for Linux, as described on this page of mine. Using EasyUEFI is probably the easiest solution to the problem, followed by using bcdedit or installing rEFInd.

Note also that some computers have buggy or quirky EFIs that require extra steps to get them working. IMHO, if the computer is new enough, it's best to return it to the store for a refund rather than accept such a defective product, but few people do so.

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AFAIK Ubuntu (and most other varieties of Linux-type operating systems) can interact with NTFS partitions but MS-Windows will not load into a Linux controlled environment. One work-around would be to install MS-Windows onto a new, clean (maybe external) drive using the BIOS setup to make that the first bootable drive. Once MS-Windows is running OK then restart from a Linux bootable USB or DVD to install the Ubuntu system onto the new MS controlled drive. The Ubuntu system on the new drive would be able to access the files on the old drive and could be used to transfer them across to the new drive.

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  • Windows will certainly install to a computer that already contains Linux, although there are caveats concerning boot loaders, as described in my answer. Installing Windows and then re-installing Ubuntu, as you describe, might work around the problem, but if you don't understand the difference between BIOS-mode and EFI-mode booting, there's a significant chance that you'll run into an equivalent problem when trying to install Ubuntu. Thus, I don't recommend trying this without first reading up on that difference -- and with that knowledge in hand, there are easier solutions. – Rod Smith Sep 21 '16 at 14:04

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