Question ASRock B450 Gaming-ITX/ac - CSM Legacy to UEFI Secure


Nov 5, 2020

I'm trying to turn secure boot on, but when I do, it seems the motherboard no longer recognizes my NVME drive as a boot drive. Am I doing something wrong, or have I just started wrong and cannot go back?
So my boot options in bios are currently set to CSM / Legacy. If I change it to Ultra Fast UEFI it doesn't seem to see the NVME and boots into BIOS. Then I turned on Secure Boot in that new setup and it still boots to BIOS.
It sees the NVME still with those settings turned on, but I'm not sure what's going on.

HALP! :p

The computer has been up and running for a year or two now.

Operating System
Windows 10 Home 64-bit
AMD Ryzen 7 3700X 46 °C
Matisse 7nm Technology
32.0GB Dual-Channel DDR4 @ 1599MHz (16-18-18-36)
ASRock B450 Gaming-ITX/ac (AM4) 42 °C Ver P5.20 (latest, I believe)
CB272 (1920x1080@75Hz)
CB272 (1920x1080@59Hz)
12272MB ATI AMD Radeon RX 6700 XT (Unknown)
931GB Samsung SSD 970 EVO Plus 500GB (Unknown (SSD))
Optical Drives
No optical disk drives detected
AMD High Definition Audio Device


Mar 2, 2023
How desperate are you to enable Secure Boot in Windows 10. Yes, it does provide additional protection, but you can manage without it. In Windows 11, Microsoft insists you enable Secure Boot and TPM, before thay allow a "standard" installation to proceed. Windows 10 permits a more "relaxed" attitude to security.

If you originally installed Windows 10 with MBR (Master Boot Record) partitioning as opposed to GPT (GUID Partition Table) and the BIOS set to CSM/Legacy, then you probably don't have a hidden 100MB EFI System Partition on the NVMe drive (use Windows Disk Management to check).

When you disable CSM/Legacy and select UEFI, Windows cannot start because the 100MB EFI System Partition is missing.

Personally, I'd just accept the lack of Secure Boot and carry on using Windows 10 as it is. Your computer will be slightly less secure and maybe a fraction slower to boot up, but if you keep plenty of offline backups, who cares?

There are tools that can change MBR partitions to GPT partitions without deleting all data, but you risk wiping your C drive if you make a mistake. Check out Easus Partition Master.

I'd be inclined to unplug the existing boot drive, fit a new SSD and perform a fresh install of Windows 10 after setting the BIOS to UEFI. Yes, it will take a few hours to re-install all your programs, perhaps even half a day, but it's safer than accidentally wiping your existing C: drive when converting MBR to GPT.

I've not tried cloning/copying partitions from an MBR disk to a GPT disk, so I cannot say if you'll be successful in getting it to boot UEFI. If you have a spare NVMe drive, give it a go, provided you don't make any permanent changes to your original boot drive's partition type.

No doubt there are some partitioning experts here who can help.


Nov 5, 2020
You sound like you work in IT.

Thanks for your reply. GPT/GUIT partitions have many benefits over MBR - performance and data integrity. Once I saw that I was for sure interested and I'm glad I did. See imgur below...

I bought EaseUS Partition Master lifetime. I've been using it here and there to build computers over the last few decades, so I thought I would give it a shot. Took all of about two minutes and two reboots. The software even reminded me to switch to UEFI boot. Easy Peasy! I have a NAS so I don't store anything of value locally so I don't have to ever worry about data loss. (I work in IT - Programming/ Server Admin Software)

Looks like I gained quite a bit of performance by switching to GPT. I may align to 4k (EaseUS) and test again.

I was hoping I would get the 1-2 sec boots like the last tow computers I build for my friends. LOL maybe it's the gen3 x3(mine) vs gen4 x4(theirs) PCIe NVME?

...LOL maybe it's the gen3 x3(mine) vs gen4 x4(theirs) PCIe NVME?
I think more likely is those were new Windows installs, so running in a clean environment with Fast Startup still working properly. Once you get the system cluttered with all those things that makes it a true "Personal Computer" it can take a bit longer to get to the desktop.

But IMO, anything under 10 seconds is great, and you should be able to see that even without Fast Startup, which is forever buggy, enabled.