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I have a tripleboot system having Windows8.1, Windows 10 and Ubuntu 15.04. When I choose Windows from grub menu, it takes me to Windows bootloader giving choice between Windows 10 and Windows 8.1. How can I configure grub such that it gives options for WIndows 8.1 and Windows 10 separately on grub menu and each option boots respective Windows directly bypassing the Windows bootloader completely? I would like to keep the Windows bootloader option also there in case I need to troubleshoot my Windows installations. The system uses BIOS.

  • UEFI or BIOS. Not sure if possible with UEFI. But with BIOS if both Windows are in primary partitions, you can repair the second install by adding bootmgr & BCD. With UEFI you may be able to create a second Windows efi folder with the Windows files & edit BCD for second install, but that is theorical as I have never seen it done. Updates may then be an issue. – oldfred May 29 '15 at 13:58
  • The system uses BIOS. – Yogesh Yadav May 29 '15 at 14:14
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    Can you expand your answer with details on how to do this using BIOS? – Yogesh Yadav May 29 '15 at 14:15
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If both Windows are in primary partitions, you can repair install to be directly bootable from grub. But not possible if an install is in a logical partition as Windows only boots from primary partitions. Second installs of Windows normally overwrite the boot files in the existing NTFS primary partition with the boot flag. And it adds both installs to its BCD. You may just be able to copy bootmgr & /boot/BCD to second install and edit BCDs in both installs. But best to have repairCD or flash drive for each install and run its repairs. You have to move boot flag first and then repair an install. You may have to specify not to find other installs. Then move boot flag to other install and do same thing.

Be sure to have good backups first. And repair tools.

To get each MS to have its own boot loader make a second primary NTFS partition and set its boot flag on, then install the 2nd product in it. Multibooters, Pictures here worth 1000+ words - Vista but all Windows with BIOS/MBR

http://www.multibooters.co.uk/multiboot.html

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