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Legacy vs UEFI

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This is not a problem, just my experiences.

I have two almost identical PCs running Windows 10 Pro 64bit.
First was upgraded from Windows 7 and is Legacy (BIOS) boot.
Second was clean install and is UEFI boot. Both run ATI 2019.

I have never had any boot related problems with the Legacy boot machine. Windows updates with multiple reboots work fine. ATI backup and recovery run trouble free.

The UEFI machine has had multiple boot related problems, one being a disaster. Responders in this forum saved my bacon and I avoided a total loss of data.

There are tons of articles on the Internet on converting Legacy to UEFI but not converting UEFI to Legacy. So, I guess I am stuck with UEFI. At least I have one machine that can be used to help fix problems on the UEFI machine.

If I had only one PC with UEFI boot, I would be in big trouble.

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Good feedback code warrior.  Unfortunately, legacy/MBR bios are being a dying breed.  Pretty much all new PC's from 2015 forward come with UEFI bios and a default OS install as UEFI on a GPT formatted disk.  

Granted, if the bios allows for the owner to enable legacy/MBR, they could reinstall cleanly and start with legacy/MBR too, but that's probably more work than most want to put in... especially if they have a finely tuned user profile with all exact apps, settings and data already configured.

In most cases, you can convert from legacy/MBR to UEFI/GPT (assuming the bios supports it and you can get past any bios firmware nuances that vary so much from system to system). 

Acronis (and most tools) won't let you revert from UEFI/GPT back to legacy - actually some will, but in general, they will not remain bootable!

However, one tool that I've successfully done this with is Minitool PartitionWizard Pro (paid version, not the free one). I've tried other free software and have not had success - sure, you can convert the drive, but not retain bootability in most cases.  

Minitool doesn't recommend you do this, but I've tried it a few times and it worked out. 

https://www.partitionwizard.com/help/convert-gpt-disk-to-mbr-disk.html

If you do decide to try it...

01) make sure you have a current and good full OS disk backup!!!! You may have to restore it. 

02) if possible, restore the backup to a different test disk (remove the original and put it away for safekeeping in case you need to return to this disk again).  Then boot the backup disk and test the Minitool conversion.  Go back into your bios, make the necessary changes for the boot order or whatever is needed to allow legacy/CSM booting (things like turning off secureboot, etc). 

If things don't work out, then go back to the original disk and working bios settings and it is what it is unless you want to rebuild.