MBR comes out of the first PC BIOS that supported booting from a hard drives. That must have been the PC/AT. Partitioning under MBR is purely a function of the OS and its boot loader. It isn't part of the hardware or BIOS. So your questions should be referencing a particular version of a particular OS. Not really a Linux question. What OS are you trying to bring back from the dead? This is what the BIOS did: in 16-bit mode it loaded the first "sector" of the disk (128 bytes) and jumped to the first byte. That's it. The rest came out of the OS's bootloader(s). DOS created the convention of using the last part of boot sector as a partition table. Some other OSes continued the convention. The boot loader and everything that came after it could make calls on the BIOS for various tasks, but only in 16-bit "real" mode. Some devices (eg. add-on disk controllers) had BIOS extensions to operate their hardware. The DOS partition table references 512-byte disk sectors. The best represenation, reached some years, was LBA (Linear Block Address). These were limited to 32 bits so at most 2 ^ 32 sectors could be used. That limited disks to 2TB, pretty small by today's standards. <https://learn.microsoft.com/en-us/troubleshoot/windows-server/backup-and-storage/support-for-hard-disks-exceeding-2-tb> Advanced Format was a complicated and painful move to 4096-byte sectors. I don't think MBR made it. I think that real (not emulated) DOS requires MBR. <https://en.wikipedia.org/wiki/Advanced_Format> Rules for partition tables are determined by your OS. Linux tended to folow whatever MS DOS or Windows did.
From: CAREY SCHUG via Talk <talk@lists.gtalug.org> To: GTALUG Talk <talk@lists.gtalug.org> Cc: CAREY SCHUG <sqrfolkdnc@comcast.net> Date: Mon, 13 Oct 2025 08:11:15 -0500 (CDT) Subject: [GTALUG] Re: history question on dos partiton tables
Thank you steve, "what you said".
Plus, there *IS* a large community of archeologists, for whom the term "computer game" is nostalgia, NOT a 3-D graphics FPS shoot-em-up. We want to resurrect or recreate old hardware, and we still want to be able to take disks back and forth between old and new hardware, run virtually on new hardware, and be prepared for any compatibility issues we haven't thought of.
And, in my case, having forgotten so much of what I "knew" back in the 1980s (and getting confused between mainframe and personal computers). For others, never having been there.
Carey
On 10/13/2025 5:03 AM CDT Steve Litt via Talk <talk@lists.gtalug.org> wrote:
D. Hugh Redelmeier via Talk said on Sun, 12 Oct 2025 10:18:00 -0400 (EDT)
Why do you ask?
It seems to me that this is only of archaeological interest these days.
It's very much relevant today. If you don't want that UEFI mess, you need to format the boot disk with the old MSDOS partitioning scheme that Carey described almost exactly, so that you can boot to an MBR. Assuming your motherboard allows you to do that.
And yes, I know that some motherboards can recognize the faux MBR on a GPT formatted drive, but that's not always the case.
SteveT
Steve Litt
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