Convert Windows 10 from Legacy BIOS to UEFI without Data Loss  

NavyLCDR said:

Look for an option to enable/disable CSM mode. Why is there a need to change it, though?

The computer is running fine, but my understanding is that with UEFI fully enabled, it would be more secure and have faster startup and shutdown, and probably some other benefits that I'm not aware of.

NavyLCDR said:

Not really. Only more secure at boot time, if secure boot is enabled. The other benefits are the ability to utilize all the space on a drive >2TB in size and have more than 4 primary partitions. Does the computer have a drive >2TB and does the owner need more than 4 primary partitions on the drive?

It only has one drive which is nowhere near 2TB, and doesn't need extra partitions. I do enjoy fixing and upgrading computers, and I was intrigued by how easy the transition to GPT/UEFI would be using MBR2GPT. But with your advice, I'll just leave well-enough alone! One less thing for me to do.
Thanks, Navy!

Hi Shawn, friend of mine who I am helping with windows, recently got an Acer Aspire 6 a615-51-51v1 with UEFI and restored W10 to legacy BIOS because she used an old emergency USB from a friend. Then she downloaded a fresh install of W10 x64 Home Single Language following the 10 Forums tutorials I sent her and used a new FAT32 USB to install that, said she changed BIOS to UEFI before booting but ended up legacy again (see picture)

I advised to do it all over again, should she run diskpart first to convert MBR to GPT disk? Or will the W10 install process overwrite the legacy MBR partition? Is it possible that her mbo/HDD is not UEFI compatible (1 year old model, hard to believe)?
Thanks
Frank

FrankW said:

Hi Shawn, friend of mine who I am helping with windows, recently got an Acer Aspire 6 a615-51-51v1 with UEFI and restored W10 to legacy BIOS because she used an old emergency USB from a friend. Then she downloaded a fresh install of W10 x64 Home Single Language following the 10 Forums tutorials I sent her and used a new FAT32 USB to install that, said she changed BIOS to UEFI before booting but ended up legacy again (see picture)

I advised to do it all over again, should she run diskpart first to convert MBR to GPT disk? Or will the W10 install process overwrite the legacy MBR partition? Is it possible that her mbo/HDD is not UEFI compatible (1 year old model, hard to believe)?
Thanks
Frank

The screenshot that you have posed shows a UEFI installation. Look at the second partition on disk 0, what does it say it is? It says EFI System. You don't get an EFI System partition on a legacy BIOS install.

Thanks NavyLCDR, the picture looked so different from my EFI partitions so I assumed it was legacy, completely overlooked UEFI
Frank

Hello,
My case is similar with the one posted under #2, but somehow the solution doesn't work in my case.
Some background: I migrated my Windows 10 installation from HDD to Samsung SSD and currently booting from there. Yesterday when attempted to upgrade to the new 2004 version it turned out that the MBR layout is a problem.
So I tried mbr2gpt tool, but unfortunately ended with the following:
PS C:\Users\XXXXX> mbr2gpt /validate /allowfullos
MBR2GPT: Attempting to validate disk 3
MBR2GPT: Retrieving layout of disk
MBR2GPT: Validating layout, disk sector size is: 512 bytes
Cannot find OS partition(s) for disk 3



The last attempt from setupact.log:

2020-05-31 22:03:30, Info MBR2GPT was explicitly asked to run in full OS mode.
2020-05-31 22:03:30, Info MBR2GPT: System disk number is 3
2020-05-31 22:03:30, Info MBR2GPT: Attempting to validate disk 3
2020-05-31 22:03:30, Info MBR2GPT: Retrieving layout of disk
2020-05-31 22:03:30, Info MBR2GPT: Initial partition information
2020-05-31 22:03:30, Info ===========================================================
2020-05-31 22:03:30, Info Partition layout for disk: 3
2020-05-31 22:03:30, Info Partition style : MBR
2020-05-31 22:03:30, Info MBR signature: 3135225746
2020-05-31 22:03:30, Info Number of partitions : 2
2020-05-31 22:03:30, Info ===================PARTITION===============================
2020-05-31 22:03:30, Info Number: 1
2020-05-31 22:03:30, Info Type: 7
2020-05-31 22:03:30, Info Boot: Yes
2020-05-31 22:03:30, Info Recognized: Yes
2020-05-31 22:03:30, Info Style: 0
2020-05-31 22:03:30, Info Offset: 1048576
2020-05-31 22:03:30, Info Length: 510992200704
2020-05-31 22:03:30, Info Volume: \\?\Volume{badfbf92-0000-0000-0000-100000000000}\
2020-05-31 22:03:30, Info Drive: C:\
2020-05-31 22:03:30, Info NT Path: \Device\HardDisk3\Partition1
2020-05-31 22:03:30, Info ===================PARTITION===============================
2020-05-31 22:03:30, Info Number: 2
2020-05-31 22:03:30, Info Type: 39
2020-05-31 22:03:30, Info Boot: No
2020-05-31 22:03:30, Info Recognized: Yes
2020-05-31 22:03:30, Info Style: 0
2020-05-31 22:03:30, Info Offset: 511581356032
2020-05-31 22:03:30, Info Length: 527433728
2020-05-31 22:03:30, Info Volume: \\?\Volume{badfbf92-0000-0000-0000-a01c77000000}\
2020-05-31 22:03:30, Info Drive: None
2020-05-31 22:03:30, Info NT Path: \Device\HardDisk3\Partition2
2020-05-31 22:03:30, Info ===========================================================
2020-05-31 22:03:30, Info ESP partition size will be 104857600
2020-05-31 22:03:30, Info MBR2GPT: Validating layout, disk sector size is: 512 bytes
2020-05-31 22:03:30, Info BCD: Opening store. Flags: 0x0
2020-05-31 22:03:30, Info BCD: Store path: "\??\GLOBALROOT\device\harddisk3\partition1\Boot\BCD"
2020-05-31 22:03:30, Info BCD: Failed load key BCD00000000. Flags: 0x40 File: \??\GLOBALROOT\device\harddisk3\partition1\Boot\BCD Status: c0000022
2020-05-31 22:03:30, Info BCD: Loaded hive at BCD00000001
2020-05-31 22:03:30, Error BCD: A valid store must have a description key.
2020-05-31 22:03:30, Error BCD: Failed to open description key for store. Store: \??\GLOBALROOT\device\harddisk3\partition1\Boot\BCD StoreKey: BCD00000001 Status: c000015c
2020-05-31 22:03:30, Error BCD: BcdOpenStore: Failed to add store from file \??\GLOBALROOT\device\harddisk3\partition1\Boot\BCD. StoreFlags: 0x0 Status: c000015c
2020-05-31 22:03:30, Error FindOSPartitions: Cannot open BCD for boot volume. Error: 0xC000015C
2020-05-31 22:03:30, Error Cannot find OS partition(s) for disk 3

Any ideas are appreciated.

Brink said:

Hello @explorerv, and welcome to Ten Forums.

I would recommend to disconnect all hard drives other than the Windows disk to avoid anything mistakenly happening to them.

Next, I would go ahead and extend the Windows "C" drive into the unallocated space to combine them into the "C" partition.

Extend Volume or Partition in Windows 10

Afterwards, try again to see if it may allow you to convert to UEFI.

Hi Brink,

Thanks for the prompt response! I tried this, and the unallocated space on disk 3 left from my attempt to manually make space for the ESP partition, which turned out to be unnecessary.
So from my perspective the issue lies in the errors at the bottom of the log, but googling them didn't give me any feasable answers, at least on the first couple of pages.

2020-05-31 22:03:30, Error BCD: A valid store must have a description key.
2020-05-31 22:03:30, Error BCD: Failed to open description key for store. Store: \??\GLOBALROOT\device\harddisk3\partition1\Boot\BCD StoreKey: BCD00000001 Status: c000015c
2020-05-31 22:03:30, Error BCD: BcdOpenStore: Failed to add store from file \??\GLOBALROOT\device\harddisk3\partition1\Boot\BCD. StoreFlags: 0x0 Status: c000015c
2020-05-31 22:03:30, Error FindOSPartitions: Cannot open BCD for boot volume. Error: 0xC000015C
2020-05-31 22:03:30, Error Cannot find OS partition(s) for disk 3