Booting Windows 10 to GPT disk using UEFI

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I'm trying to understand what it means to boot into a GPT-initialized disk on UEFI system.

In the world I live in Windows only boots to MBR disks. But I keep reading that it is possible to boot using GPT. Few questions arise:

  1. UEFI seems to exist only if the hardware supports it. How do I check if my (new PC, HP Z440) has it?
  2. How does booting to GPT work (there's no boot record!)?

The real reason I bring all this up is because I am trying to install Windows 10 onto a brand new SSD (OWC). I failed. Here are the details:

  1. When 1st plugged in, the motherboard didn't even recognize the SSD
  2. Then I plugged it in via USB and it was seen. I mirrored my existing drive onto using Acronis
  3. When I plug it back into SATA and try to boot, I get irql_not_less_or_equal error (which is a driver error, when it tries to access an illegal memory address space, from I've read)
  4. I'm trying to update the firmware on the drive now, which could be a solution

I am exploring options to get this fixed, thus the questions about using GPT.

Edited by yegorski

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Z440 and anything modern (Haswell and up) usually supports UEFI out of the box. Heck I think it goes as far back as Ivy Bridge for easy support (aka it's always going to be a UEFI).

There's nothing to set for a fresh install, it generally all works out of the box. Plug in your SSD, enter the UEFI setup to make sure the SSD shows up properly in the boot order, and then when you plug in Windows 10 installation media and reboot, when you check boot options, your Windows 10 installation media should show as an item under UEFI boot order. You're set.

I mirrored my existing drive onto using Acronis

You'll need to Google your exact error with regard to drive cloning, but sounds like a driver configuration error.

Which SSD exactly is this? Also if you cloned your existing drive, is your existing drive MBR? If it's MBR and you cloned it then the SSD will be an MBR disk as well, so there's no need to worry about GPT. If the drive you cloned is GPT then it's already working as GPT and your issue is not GPT related...?


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Thanks for the reply.

I worked-around my problem by installing WIndows 10 fresh on the new SSD. Formatted during Win10 installation. No errors.

I DID, however have to specify boot type "Legacy" in the BIOS. From what I understand, legacy is not UEFI? (I still don't what UEFI means in terms of booting).


The SSD was from OWC, which is a company focused on hard drives for Mac (I forget which SSD exactly I ordered from them). So perhaps this is an OWC-related issue.

Side note: what's curious is that Acronis support said that they software is not able to clone to SSDs... I have a hard time believing that.


PS: HP Z440 (and their other models) have Windows 10 key burned into the mobo. So I was able to reinstall same version of Win10 (Pro) without entering a key.

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Legacy is not UEFI. You should have seen both a UEFI and a Legacy option in the system boot menu. Heck I just setup a Z440 a few months ago, unfortunately I no longer have access to that box so I can't take any screenshots for you.

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