4 ms·
>The MBR checked which of the 4 possible primary partitions was flagged as active, and then booted control to the Volume Boot Record (Boot Sector) residing at t
by jaclaz 4y ago
>The MBR checked which of the 4 possible primary partitions was flagged as active, and then booted control to the Volume Boot Record (Boot Sector) residing at the first sector of that particular partition which would then (usually, but specifically according to BOOT.INI on Windows [BCD today] or GRUB configs for Linux) load the OS contained within that partition. Usually by reading files from the filesystem beyond that point, but capable of being chained directly to other executable sectors.
You forgot the Windows boot manager, on Windows NT the chain is:
Up to XP:
BIOS->MBR->PBR of active partition->NTLDR (+NTDETECT.COM)->BOOT.INI->Choices->OS
Vista and later:
BIOS->MBR->PBR of active partition->BOOTMGR->\boot\BCD->Choices->OS
The MBR only passes control to the PBR and the PBR only loads the Windows boot manager, it is this latter that does all the actual OS loading and that reads BOOT.INI and \boot\BCD settings and user choices.
- fuzzfactor 4y agoGood to see your message jaclaz. You're another one like Starman who can fill in details like no-one else, in case people are not aware. Please kindly post a link to the message board where your most valuable information still can be found! What I'm seeing now is when Windows 8+ is installed to an MBR partition, and boots normally from a plain NT6 BOOT folder using BOOT\BCD in legacy CSM mode no differently than Vista (whether the boot folder is on a separate hidden volume or the same partition as Windows itself), the same Windows files on that partition can also boot using UEFI if available, from an alternative EFI\BOOT folder (plus accompanying EFI\Microsoft\BOOT\BCD) on the same or similar media. In the first case with BIOS it ends up running winload.exe, but under UEFI the firmware runs winload.efi instead, since both the "DOS" executable and the EFI executable are both present in the Windows\System32 folder, you have your choice here too.
- jaclaz 4y agoThanks for the comparison, though of course the Starman's site is a much better source than my scattered posts, mainly on: https://msfn.org/board/ https://msfn.org/board/ and: http://reboot.pro/ http://reboot.pro/ (on this latter under the nick of Wonko the Sane) About your Windows 8+ report, yes, what you describe is perfectly normal, what many people tend to forget is that UEFI does not necessarily means GPT, a UEFI can access "MBR style disks" just fine (the opposite, BIOS acccessing a GPT disk needs special provisions, so-called hybrid MBR's and "special" code in them). You evidenced however yet another aspect of more recent NT Windows booting, until XP NTLDR was both the boot manager and the OS loader, now BOOTMGR (and bootmgr.efi) is just the boot manager and it chainloads a separate OS loader, the WINLOAD.EXE (or winload.efi).