Changing System Drive from GPT to MBR

Question

I currently have an Acer Laptop running Windows 10.

My system drive currently has a GUID Partition Table (GPT) but I want to convert it to MBR Partition Table. Doing this wont be a problem as I found plenty of tutorials.

I am completely new in this area and have no idea what will change if i do this. Will I break something on my computer?

The reason I want to do this is because I wish to use Veracrypt to encrypt the entire system partition, rather then encrypting individual containers and veracrypt only supports MBR.

The Questions:

• What are the advantages/disadvantages of doing such modifications

• Is there a likelihood something will break? What should I look for

• Is there anything else I need to be aware of?

Thanks

Solution

Taking your questions out of order:

• Is there a likelihood something will break? -- Yes. Your computer WILL NOT BOOT after doing this conversion if you do it in-place with a third-party tool. There are ways to restore the system to bootability after such a conversion, but I don't happen to have any references handy. If you do it by backing up, re-installing, and then restoring your personal data, your computer will boot, but you'll have to be careful of how you do it; there are numerous pitfalls if you don't thoroughly understand what you're doing -- which you clearly don't, else you wouldn't be asking this question.
• What are the advantages/disadvantages of doing such modifications -- You've stated the only real advantage to doing this in your case -- namely, you can use the encryption software you want to use. I'm not familiar with Windows encryption software, so I can't suggest any specific alternatives; but I recommend you look for such an alternative and give serious consideration to using anything you might find rather than something that works only with the outdated MBR partitioning system. New PCs have been shipping with GPT since Windows 8.0 was released, so if software supports nothing but MBR, that suggests it isn't being well maintained -- a serious issue in a security tool.
• Is there anything else I need to be aware of? -- Windows ties its boot mode to the partition table type -- using GPT, Windows boots only in EFI/UEFI mode; and using MBR, it boots only in BIOS/CSM/legacy mode. This means that switching from GPT to MBR also means switching from an EFI-mode boot to a BIOS-mode boot, which has several implications:
  • This change is the cause of Windows no longer booting if you do it in-place; you must install a BIOS-mode boot loader.
  • You must activate the Compatibility Support Module (CSM) in your firmware. Most, but not all, computers have a CSM. You should check for this option (usually called "CSM" or "legacy boot support" in your firmware) before you invest more time.
  • Getting the Windows installer to boot in a particular mode can be tricky, and the details of how you force a particular mode vary from one computer to another. As a general rule, you need to activate the computer's built-in boot manager and select the boot option for the boot medium that does not include the string "UEFI."
  • You won't be able to use Secure Boot if you switch to BIOS-mode booting. Secure Boot is designed to make it harder for malware to take over the computer before Windows boots.
  • If you're using a manufacturer-provided installation of Windows, chances are its installation and recovery utilities support only EFI-mode booting. You'll therefore have to obtain a more generic "retail" version of Windows to install it in BIOS/CSM/legacy mode.

Overall, your plan is one that's likely to lead to headaches. It may be worthwhile if you really need your particular encryption software; but I recommend looking into alternative encryption tools before taking this path.

Comments

[cybernard]

Also: MBR does support hard drives greater than 2TB. (approx)

[Rod Smith]

Well, yes and no. The 2TiB limit is really 2^32 * (sector size) bytes, so it goes up if the sector size goes up, as is the case for a small number of internal disks and many more external (USB) disks. It's also possible to start a 2TiB partition at just under the 2TiB limit, thus extending the capacity addressable by MBR to just under 4TiB; but this doesn't work in all OSes and is not supported by all utilities, so it's a rather risky "hack," not a dependable MBR feature. See this page of mine for more on these topics.