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I have installed Win 7 on a Win XP computer as second operating system. After Win 7 had been installed the partition boot record of logical drive which win XP was installed on and bootmgr file has been created on the same drive, as expected. Does Installing Win 7 make other changes on the partition XP installed on? If original Win XP installation is restored from an image, is it possible to restore dual boot by just copying that bootmgr and rewriting pbs (partition boot sector) sector of the partition which Win XP installed on, after XP restoration?

I explain more:

I have a hard drive.

I have partitioned it -> After then logical drives C and D have been created.

I installed Win XP on C -> In this condition, partition boot sector (NTFS Boot Sector) of the C logical drive loads NTLDR to load operating system.

I installed Win 7 on D for dual-boot-> In this condition, the partition boot sector of the logical drive which Win XP installed on has been changed; now it loads BOOTMGR first, instead of NTLDR. And a file has been created in the drive which Win XP installed on: BOOTMGR.

I would like to learn if installing Win 7 as a second operating system for dual-boot made any other changes on the drive Win XP installed on and if I restore Win XP installation from an image of original XP installation, is it possible to restore a dual-boot just restoring the pbs to the situation after Win 7 installed and copying that BOOTMGR file to drive which XP installed on.

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  • If you are talking about the same drive using the MBR partitioning scheme, then the active partition also plays a role.
    – Señor CMasMas
    Commented May 17, 2021 at 4:26
  • @Señor CMasMas Sorry, I've edited the question. I mention not the mbr of physical drive but pbs of logical drive.
    – kitap mitap
    Commented May 17, 2021 at 4:33

1 Answer 1

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The installation of Windows 7 in dial-boot has placed bootmgr and BCD (boot configuration data) files inside the partition of the existing XP installation.

The process of booting Windows 7 has now become:

enter image description here

The software in the Partition Boot Record (PBR) is not sophisticated enough to understand disk formats or directories/files.

For Windows the PBR loads an additional 16 sectors from the beginning of the partition. These sectors constitute the first stage of the Windows boot loader which in turn loads one of two files depending on the version of Window:

  • For versions of Windows up to XP, the file NTLDR is loaded into memory. PBR then transfers to NTLDR.

  • For Vista and subsequent versions of Windows, the PBR loads bootmgr, the Boot Manager, into memory and transfers to that.

First, the BCD is also modified, in addition to bootmgr.

But more important, the correct dual-boot depends on the bootmgr file that is known by its physical address on the disk.

This means that you cannot just copy back the original XP installation, then modify it by copying bootmgr to it, since you don't have the ability to move it to an exact physical address on the disk.

The answer is then negative: Restoring the original XP installation would require the re-installation of Windows 7, to setup bootmgr in its correct address and modify the BCD.

Reference: The Boot Sequence of Dual-Boot XP & Windows 7.

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  • simple and excellent.
    – kitap mitap
    Commented May 17, 2021 at 15:29

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