How's It Possible That My Windows Boot Camp is Booting w/ an MBR

[Alvin777]

Hi Mac friends, about April of this year, Windows Boot Camp wasn't booting, usually it's the black screen of death or the boot loop (but I can mount it on macOS and copy files from it), at that time for almost a week from morning to almost midnight, I tried to make it boot (Cmd, Chkdsk, sfc, DISM, Windows auto repair using the installer, Aomei, EaseUS, other apps using I think Windows to Go; if I remember, I even took the newly brought SSD out & put it in an actual PC then put it back in the Mac coz' I had a lot of game files there that tool months and years to finish & other stuff I can't replace coz' it didn't have even a File History backup coz' macOS is my main OS for productivity), creating another Windows installation, creating flashdrive and external drive bootable stuff, including Windows to Go to fix it for a week or more, I came across a paid (I think it was at a discount when I bought it or free for a short time or for special causes) app called EasyRE by Neosmart (truly if you seek you shall find but w/ much perseverance and focus), it was the most powerful very easy to use app to make Windows boot again (though for good measure, while I can still boot, if I remember I created a Windows Recovery flashdrive/bootable Windows Installer and used the CMD there to delete the Boot Camp's MBR and painstakingly create a new one for good measure).

I noticed though Boot Camp is booting under MBR, unless it's possible if it's an internal drive, how's it booting if it's not GPT? I believe EasyRE brought it back to life, it changed its partition table from GPT to MBR if Boot Camp initially uses GPT (using the Boot Camp Assistant to format the Boot Camp partition on macOS).

 

[joevt]

Old Macs boot Windows using legacy BIOS (Boot Camp) starting from MBR. Newer Macs boot Windows using UEFI on GPT. What Mac do you have?

Usually GPT has a MBR containing a single partition of type EE that covers everything starting from the GPT partition. The actual partitions are in the GPT instead of the MBR.

In the case of Boot Camp on old Macs, the drive is GPT/MBR hybrid. On a hybrid disk, the MBR of the GPT has an EE partition that covers the blocks starting from the GPT partition and ending at the end of the EFI partition. 1 or more of the 3 remaining partitions of the MBR correspond to partitions found in the GPT. One of them is marked as the active partition which will be used for booting from MBR. You must never modify partitions using Windows because the MBR and GPT partition tables will no longer correspond correctly.
https://www.rodsbooks.com/gdisk/hybrid.html

Did the disk that EasyRE fixed contain any other partitions? Do those other partitions still exist? Before and after I do partitioning for BootCamp, I use my dumpvols.sh script to get all the info about the disks and compare to see what got changed.
https://gist.github.com/joevt/a99e3af71343d8242e0078ab4af39b6c