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I recently bought a refurbished Dell Precision 7510 running Windows 10 and decided to clone the included HHD to an NVMe SSD. In the process, I noticed my laptop's partition system was set to MBR and my laptop has been in UEFI mode all the time I have been using it. I have read in many articles a GPT partition system should always be used with EFI boot and am unsure if my refurbisher did this for a reason.

Should I convert the partition system and, if so, how should I do so in a safe way?

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    Research MBR2GPT
    – Ramhound
    Commented Mar 29, 2021 at 5:37
  • If your system is currently working then do not try to break it. Trying to convert it means knowing exactly what other things you need to change at the same time.
    – Mokubai ♦
    Commented Mar 29, 2021 at 7:05
  • UEFI and BIOS are not the same things: BIOS [Basic Input / Output System], developed in '75, is a 16bit firmware with massive limitations; UEFI [Unified Extensible Firmware Interface], developed in '05, is a 64bit firmware w/ a multitude of features BIOS is incapable of supporting (CSM mode emulates BIOS' 16bit architecture within a 32bit environment, only existing to support distros incapable of EFI boot pre-2016ish)
    – JW0914
    Commented Mar 29, 2021 at 13:49
  • Converting to GPT is always recommended with UEFI firmware, else boot performance is severely degraded; AFAIK, it's not possible to install Windows to an MBR partition table w/ CSM mode disabled, as EFI boot requires GPT partition ID c12a7328-f81f-11d2-ba4b-00a0c93ec93b (I don't believe DiskPart supports the EFh MBR partition type)
    – JW0914
    Commented Mar 29, 2021 at 13:53

2 Answers 2

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If Windows works, then everything is already configured properly. If your disk is indeed partitioned using MBR, then the UEFI is configured to emulate a BIOS and Windows boots as if it was a BIOS. We know that because Windows supports MBR only when booting in BIOS mode and GPT only when booting in UEFI mode. It's not broken, don't fix it.

If you want to convert to GPT for some reason, the mbr2gpt tool can do that if your system satisfies a few requirements. But if you don't have any actual problem that you're trying to solve, I'd advise to keep it as it is.

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  • Converting to GPT is always recommended w/ UEFI, else boot performance is severely degraded; AFAIK, it's not possible to install Windows to an MBR partition w/ CSM mode disabled, as EFI boot requires GPT partition ID c12a7328-f81f-11d2-ba4b-00a0c93ec93b (I don't believe DiskPart supports MBR partition type EFh). CSM mode only exists to support distros incapable of EFI boot pre-2016ish
    – JW0914
    Commented Mar 29, 2021 at 14:01
  • @JW0914 You're right, but since OP isn't complaining about boot times I'd rather advise them to stick to MBR+CSM rather than risk breaking something for no good reason.
    – gronostaj
    Commented Mar 29, 2021 at 14:06
  • I understand that perspective and while I've never used mbr2gpt, simply capturing a WIM of the OS partition prior to using it would negate all potential risks
    – JW0914
    Commented Mar 29, 2021 at 14:08
  • So in short I should research mbr2gpt and creare a WIM of my OS to make a successful translation to GPT
    – james
    Commented Mar 29, 2021 at 17:37
  • @james If you need GPT. There's nothing wrong with MBR. GPT has its advantages, but MBR is already there and it's working, that's a big plus. If you want to convert anyway, I'd personally go with some disk cloning software rather than WIMs. A competent cloning/imaging tool will let you restore the whole disk without any extra tinkering. With WIMs you can only capture partition contents, but not their layout and boot config.
    – gronostaj
    Commented Mar 29, 2021 at 18:17
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UEFI firmware can install Windows 10 to MBR, but the UEFI BIOS must be set to Legacy Mode. Without Legacy Mode, only GPT is allowed for Windows 64-bit.

MBR is just as good as GPT. The only advantage of GPT is that it allows using hard disks of more than 2 TB.

Note that Windows can use a GPT disk in Legacy Mode, as long as this is not the system drive. An additional disk can be in GPT format.

Converting between MBR and GPT via Windows will destroy the disk's contents. Third-party utilities exist that can do the conversion without data-loss, but it's still advised to make a disk-image backup in case it fails.

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  • UEFI and BIOS are not the same things (context matters in this case)
    – JW0914
    Commented Mar 29, 2021 at 13:09
  • @JW0914: There is still some confusion in terms. Many people say BIOS when they mean the UEFI firmware, and even some UEFI firmwares do this error. It's a problem when writing an answer that the poster will comprehend.
    – harrymc
    Commented Mar 29, 2021 at 13:13
  • OEMs conflate the two to consumers and we should be better than that: BIOS [Basic Input / Output System], developed in '75, is a 16bit firmware with massive limitations; UEFI [Unified Extensible Firmware Interface], developed in '05, is a 64bit firmware w/ a multitude of features BIOS is incapable of supporting (CSM mode emulates BIOS' 16bit architecture within a 32bit environment, only existing to support distros incapable of EFI boot pre-2016ish)
    – JW0914
    Commented Mar 29, 2021 at 13:48

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