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this is the situation: I had an old PC running on bios and only MBR, I had bought a SSD for it and migrated the updated windows 10 to it and it was working fine. So I decided to build a new PC but to keep my old data. couple of HDD's and of course the SSD. In my new build I installed a NVMe memory for speed sake. after completing build, when I turned on the PC there was no sign of old windows 10 in boot options. I had prepared a windows 11 installation media hoping to upgrade the windows 10. But it said that it is not possible to upgrade from bootable media. So I just installed win 11 to NVMe and it is working. I changed the SSD mbr to gpt but it doesn't show up in boot option again!. I searched how to bring back the booting option to SSD win10 installation but no useful solution. Many programs and settings are already on the win 10 install. so I just want to upgrade it to 11 and then migrate it to NVMe

any approach to this?

A. choofe
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2 Answers2

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This article solved the issue http://woshub.com/how-to-repair-deleted-efi-partition-in-windows-7/ As my old SSD used MBR and my new UEFI MoBo does not work with those. I just convert mbr to gpt but that is not how EFI works. It needs a standard structure. The article just explain to recreate the structure if it just deleted or corrupted.

But not in my case where there was not any structure before. so I managed to create those partitions needed with the help of partition managing programs in my other OS (win11). Just need to create a 100 MB efi partition + 16 MB (in case of win 10. needs 260MB for previous windows) and then the main partition in which windows is installed.

just keep in mind that there will be a 1 MB offset between those two, so you need 117 MB in the beginning of the drive. after creating that free space before the windows partition you can continue with the article. the trick with diskpart is to use offset parameter with create partition command to make needed partition in the beginning of the drive. size is in MB and offset is in KB (KibiByte). first partition needs offset of 1024 KB and size 100 MB it's something like this create partition EFI size=100 offset=1024 and the second one needs offset of 103424 KB and size of 100 MB like this create partition MSR size=16 offset=103424 Important is that you have to have at least 117 MB unassigned space before windows partition. after creating these partitions go with the instruction of the article

A. choofe
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  • As it’s currently written, your answer is unclear. Please [edit] to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers in the help center. – Community May 07 '22 at 11:45
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From what you describe, this should be the solution: In some cases, UEFI firmware requires you to turn on an option "Legacy Boot" to be able to boot from a MBR record. Without this option, only EFI boot options are available; EFI boot works because each OS writes data into a small non-volatile memory region, the NVRAM.

  • The NVRAM is a small persistent memory area in which each operation system stores their entry point, usually consisting out of the UUID of the boot partition, plus the path to the .efi file; this entry point is invalidated after you move the OS to a different partition/change the partitioning format and is why the OS cannot be found any more

Both Windows 10 and Windows 11 should have boot repair options, probably when booting from the installation media.

JW0914
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Martin
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    can a windows to go do the boot repair? cause I got a windows to go wim file – A. choofe May 04 '22 at 08:54
  • I have never used "windows to go", so I do not know. But it should... – Martin May 04 '22 at 08:58
  • Oh another thing. Can windows 11 installation media do the repair as well? on the win 10 install corrupt boot drive I mean – A. choofe May 04 '22 at 09:06
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    CSM Mode should never be enabled for an OS, as its sole purpose was to support distros [BSD/Linux] that didn't yet support EFI boot circa <2017 (Windows ≥7 supports EFI boot); CSM Mode emulates BIOS' 16bit architecture within a 32bit environment and doing so will cause performance degradation (boot times increase by 400%+, GPT can't be used, etc.). To resolve the issue, mbr2gpt to should be used convert the old OS disk to GPT. – JW0914 May 04 '22 at 12:45
  • @JW0914 Thanks. Can you clear this command for me? "c:> BCDboot d:\windows /s e:\ /f all" does this use windows boot files installed on source "e:" boot file (which in my case is an installation media" to make "D:" bootable while using windows installed on "D:\windows" ? or is it something to do with the current active drive which is "c:" by the way? – A. choofe May 05 '22 at 04:05
  • @A.choofe BcdBoot <boot files source> /s <OS Drive> /f <firmware type> (<boot files source: OS partition's Windows directory | <firmware type>: uefi, all, etc.). When booted to WinPE/WinRE, C: is usually not the OS partition (to ascertain: DiskPart → Lis Vol → Exit). %WinDir%\Boot stores a backup of all boot files for use by BootRec and BcdBoot, but these can't be used to boot the OS as they must reside on the boot partition in order to boot Windows. – JW0914 May 05 '22 at 04:17
  • @JW0914 so you mean that command I just wrote copies the boot files on d:\ to e:\ and make the e:\ bootable? the /f made that bootable to uefi or legacy bios or both that I know. I think I made a laughable mistake and used that upside down and made my installation media to load windows from my SSD. even it has the winPE. that's why I was able to boot my old windows from choosing boot from that usb. – A. choofe May 07 '22 at 09:47
  • By the way I managed to create the efi structure manually and by using bcdedit commands create the efi system. now I'm able to boot both ssd and nvme from boot up menu by pressing F8. – A. choofe May 07 '22 at 10:34