Upgrading from Windows 10 to Windows 11 on Z800

[NeilG4]

I am wanting to upgrade to Windows 11 on a Z800 with all existing files and settings kept on Windows 10. I have done this successfully on a Z840 using Rufus and Flyoobe. I am testing the USB stick to boot with DUET/REFIND into the Windows 10 OS, but I always get the message OS EFI not found.

Please can anyone help?

[Paul_Tikkanen]

I would use the approach to do an in-place upgrade from W10>W11 in this video:

It's easy and it works on older PC's.  I used it on an old HP 8200 Elite CMT business desktop that has an i7-2600 processor and doesn't support secure boot.

How to Install Windows 11 25H2 on Unsupported PCs (New Easiest Method)

[DGroves]

the z800 requires a earlier 2015 release of the DUET/REFIND application see the attached zip file which i had no trouble using on my z800 to boot a nvme drive from the created usb key connected to the z800's internal usb header

you can also see if the latest 20020 release fixes the bug that the 2017/2019 releases of DUET/REFIND had in regards to the z800

unlike the newer Zx20 models the older Zx00 is unable to use the datacenter PCI-E ssd cards that had boot code embedded in the ssd bios (like the intel (dc3700) the only two retail consumer nvme ssd's that might (untested by me) boot on a z800 were the samsung 950 pro and the original 256GB predator pci-e x2 SSD

if you are able to boot win 10 from a nvme drive on your current z800's hardware config you will need to create a win 11 usb key with the program RUFUS and select the LEGACY install------ not the default gpt option in the rufus USB KEY creation settings

the z800 is a pure legacy only system, 

the later Zx20 models had support for EFI (but no nvme boot code)

and the Zx40 models had full UEFI w/nvme boot code

[NeilG4]

Thank you both for your informative replies.

I bit the bullet and upgraded to Windows 11 with the keeping of the MBR. I had read of many folk that had done the same without any bad consequences. Obviously, I have backed up my Windows 10 system drive so if the worst happens I can always return to it.

[Paul_Tikkanen · Accepted solution]

You're very welcome.

Since the PC does not have a UEFI BIOS you can only format the drive with the MBR partition table.

I'm running W11 25H2 on an old Dell PC that does not have a UEFI BIOS, no TPM device, does not support secure boot and only has an Intel 1st gen core processor that just met the new SSE 4.2 processor requirements for W11 24H2 & 25H2.

Works fine.