UEFI with MBR partition table?

Question

I want to convert the current GPT partition table to MBR on my laptop which uses UEFI.

Is it safe it use UEFI with MBR partition table?

Maybe I am misunderstanding about UEFI/GPT things?

Solution

is it safe UEFI with MBR partition table?

You're not asking about safety, but about support. Yes, EFI firmware has no trouble with an MBR partition table, which it can cope with just as it can cope with an EFI partition table. You just need to make sure that you have an EFI System Partition.

Your problem is Windows. Microsoft erroneously conflates has a GPT partitioned disc with bootstraps in the EFI way. So your laptop with a modern EFI partition table and modern EFI firmware has been installed and is bootstrapping Windows in the modern EFI way. Change to an MBR style partition table, and Windows will expect to be bootstrapping in the old PC98 way. You'd have to switch on the Compatibility Support Module option in your firmware, if it has it, and either reinstall Windows or individually modify the Microsoft Boot Manager, the system BCD store, the system volume's VBR, and the MBR bootstrap program.

All that fuss, and a massive step backwards, just for a rather dodgy "boot logo changer" and a "Microsoft Toolkit" that's almost certainly not Microsoft's? (Some quick searches turned up various things purporting to be these. Perhaps the most appalling was the one that gave step by step instructions to the marks for turning off security, patching their system files to turn off warnings of danger, and trusting a new root certificate; roping them in with the promise of a different picture at bootstrap time. But the bogus "anti-virus" company falsely telling people that Microsoft wrote AutoKMS so they shouldn't worry their pretty little heads about it came a close second.) I suggest not.

Comments

[Admin]

MBR is not compatible with UEFI unless placed in legacy support mode. Yes; You have a massive misunderstanding about UEFI/GPT

[Admin]

@Ramhound: UEFI is required to support GPT, but not necessarily to use it – MBR partition table support is in fact a requirement for UEFI as well (section 5.2), and there is a MBR partition type for the "EFI system partition" (0xEF). What UEFI does not use is the bootstrap code contained within the MBR.

[Admin]

Apu889: Out of curiosity, what is the reason for using MBR?

[Admin]

@Ramhound: Thanks for make my mind straight. I am on Legacy mode now (Been downgraded from Windows 8 to 7 recently). AFAIK there's compability issues on some programs that require MBR partition, like Win7 Boot Logo Changer, Microsoft Toolkit, etc. And i need that. Do you recommend me to move to MBR?

[Admin]

@grawity: like a said comment above, there's some programs that still doesn't support GPT/UEFI system.

[Admin]

JdeBP's answer is pretty much spot-on, but I want to say that if your computer is booting Windows 7 from a GPT disk, you're not "on Legacy mode now." Windows ties boot mode to partition table type in a very inflexible way, so if the boot disk uses GPT, Windows is booting in EFI mode. (Windows 7 is perfectly capable of booting in EFI mode.)

[jiggunjer]

I don't think "EFI partition tables" exist.

[jiggunjer]

I think this answer contains a mistake: it assumes UEFI will always boot an MBR drive the same way as BIOS. But in fact the firmware will ignore the MBR if a usable EFI partition is available. So you can convert from GPT to MBR without the hassle mentioned; if you have the efi partition it will boot just like with GPT. Some firmware might always use legacy mode if an MBR is detected, but this behavior is not standard.