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I wanted to dual boot boot My Windows 10 with Zorin OS . I have done this before with Windows 7 . But when I tried installing EasyBCD in Windows 10 , It told me that most functions of Easy BCD wont work in Win 10 because of UEFI Boot mode .

So I went to BIOS and checked the Boot setting , There were couple of options , of which i understood none . Any help on what to do ?

Image of Boot order Options

MOBO - Gigabyte B250M-D2V-CF with Bios version F6

And if I change my Boot mode , do I have to reinstall my windows ?

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First of all, you need to get some background about the booting process. Old motherboard firmware with a BIOS program loaded use a specific sector in a disk to start from. That will contain the information for a second step etc. At one point it gets to the windows bootloader and you can edit that with EasyBCD.

Modern AMD/Intel motherboards no longer have a BIOS program in their firmware. They have an UEFI program. EFI looks for a specific partition (not a sector) and starts the loader from there. This is also where you can put a loader for your OS.

That changes the sequence of things.

Old:

  1. Firmware boots. Have saved setting to select a specific drive.
  2. Boot sector is read from a drive (basically a very small program).
  3. Boot sector program runs and usually loads a bigger program (lets call it bootload2)
  4. Bootloader 2 starts the OS (e.g. windows, or Linux, or ...)

Now you could insert a different program at point 3, then you get

  1. Firmware boots. Have saved setting to select a specific drive.
  2. Boot sector is read from a drive (basically a very small program).
  3. Boot selector program loads (e.g. GRUB).
    Depending on your choice grub then loads the bootloader2 which runs windows, or GRUB loads something else which runs Linux (or any other OS).

Now it is going to get more complicated.

The thing a generically called bootloader2 usually just loads windows, but it can also be tweaked. THis is where your EASYBSD comes in.


Abandoning this an moving to EFI (your current setup)

  1. Firmware boots. Firmload looks at the drives and find the ESP (Efi System Partition).
  2. If a file is set in the 'BIOS' *EFI loads the bootloader (e.g. bootX64.efi) on the filesystem and loads that.
  3. BootX64.efi loads windows.
  4. Windows starts up in EFI mode.

You can have multiple loaders on the ESP partition. Given a good motherboard you might even be able to select one of these when it powers up.

Alternatively you could have a EFI program which does not just load the OS, but which was which OS to boots and then transfers control to the right bootloader.



OK, plenty background. Now to one of your question.

And if I change my Boot mode , do I have to reinstall my windows?

Many EFI firmware have CSM (compatability shims). This is sometimes calls legacy mode.

If you enable this it will try to boot in the old way. That means that you will have to add a bootsectors. You will need the old bootloaders. And windows installs different parts of itself depending on how you booted. You you end up with reinstalling windows.

So "do I have to reinstall my windows" is:Yes, you end up reinstalling.

As yo how to actually solve this: Leave the firmware on EFI only. That greatly simplifies things. Next find an EFI loader for Zoron OS, the best start point I found for this is this post on our sister site. https://askubuntu.com/questions/436096/uefi-and-reserved-bios-boot-area



*Actually BIOS is a wrong name. There is neither a BIOS program present, nor do you store things in a BIOS in the classic setup. It gets stored elsewhere and read by the BIOS. But lets keep things simplified here.

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  • I didnt faced the problem discussed in the link, i was able to install the bootloaded of Zorin in my desired Partition ,But i was not able to what would you call-"create an Entry Point in windows boot loader using EasyBCD and linking it to the partition where Zorin Bootloader is installed."What I exactly want to happen and why EasyBCD only is because of this guy's method. I have done it before in my previous PC with Windows 7 . Sep 1, 2018 at 12:10
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    @BabaBlackSheep Your Win7 was BIOS, probably. As pointed out in this answer, the installation is different and the installer will put the Zorin EFI file(s) is the EFI partition automatically. You don't need to do anything else except setting UEFI to boot from Zorin's Grub instead of the "Windows bootloader". You certainly don't install any bootloader in Zorin's partition nor anywhere else. For your convenience always follow this suggestion: Leave the firmware on EFI only (and forget about old methods that are no longer relevant for newer PCs).
    – user931000
    Sep 1, 2018 at 12:51

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