What is Master Boot Record:
The Master Boot Record (MBR) is the first 512 bytes of a storage device. The MBR is not a partition; it is reserved for the operating system's bootloader and the storage device's partition table.
This page examines the Windows 7 MBR code. (We had this page near completion, but lost it during our last move in May, 2010. Now even the Windows 7 RC versions have expired! This page is still a work in progress, but you'll find interesting facts about the code and a clear layout of each assembly instruction as with all our previous MBR/VBR pages.)
Whenever you install Windows 7 to a hard disk, even one with an existing MBR, its first sector may be overwritten with the Windows 7 MBR code. (Note: If necessary, it will also change the Volume Boot Record of an existing Active Windows boot OS; usually found in the first partition of a PC's first hard disk.) This code is also installed on blank hard drives when using Windows 7's Disk Management utility.
NOTE: On our Windows 7 RC Install DVD, all 512 bytes of this MBR (including the zero-bytes in the partition table) were found in boot\bootsect.exe, sources\upgdriver.dll and sources\winsetup.dll; see below for more files containing this code.
Like all other MBRs presented in this series, this MBR code could still be used to boot any OS on some x86 PCs if it meets the conditions listed
How to Fix the Master Boot Record in Windows:
One useful and often necessary thing you can do in the Windows Recovery Console is fix a corrupt or damaged master boot record (MBR). The MBR plays a role in starting your PC and what happens when it’s damaged. Recovery is entirely possible if you can access the Recovery Console and you know which command to type for your version of Windows.
In Windows 7 and Windows Vista, type the following command at the Recovery Console prompt:
BOOTREC /FIXMBR
Type the command exactly as written: BOOTREC, a space, a forward slash, and then FIXMBR not followed by a period. Press Enter.
In Windows XP, you type the following command to fix the master boot record at the Recovery Console prompt:
FIXMBR
Press the Enter key and then press Y and Enter to confirm.
For all versions of Windows, this command works instantly. You see another command prompt displayed. Type exit to quit the command prompt. Restart the PC if it doesn’t restart automatically.
When the computer restarts, whatever problems afflicted the MBR should be gone. For example, if you were removing a boot manager program, it no longer appears when the PC first starts.
No danger is involved in fixing the MBR; if it wasn’t damaged, running the FIXMBR command doesn’t screw anything up (well, unless something else is wrong with the boot drive).
The Master Boot Record (MBR) is the first 512 bytes of a storage device. The MBR is not a partition; it is reserved for the operating system's bootloader and the storage device's partition table.
This page examines the Windows 7 MBR code. (We had this page near completion, but lost it during our last move in May, 2010. Now even the Windows 7 RC versions have expired! This page is still a work in progress, but you'll find interesting facts about the code and a clear layout of each assembly instruction as with all our previous MBR/VBR pages.)
Whenever you install Windows 7 to a hard disk, even one with an existing MBR, its first sector may be overwritten with the Windows 7 MBR code. (Note: If necessary, it will also change the Volume Boot Record of an existing Active Windows boot OS; usually found in the first partition of a PC's first hard disk.) This code is also installed on blank hard drives when using Windows 7's Disk Management utility.
NOTE: On our Windows 7 RC Install DVD, all 512 bytes of this MBR (including the zero-bytes in the partition table) were found in boot\bootsect.exe, sources\upgdriver.dll and sources\winsetup.dll; see below for more files containing this code.
Like all other MBRs presented in this series, this MBR code could still be used to boot any OS on some x86 PCs if it meets the conditions listed
How to Fix the Master Boot Record in Windows:
One useful and often necessary thing you can do in the Windows Recovery Console is fix a corrupt or damaged master boot record (MBR). The MBR plays a role in starting your PC and what happens when it’s damaged. Recovery is entirely possible if you can access the Recovery Console and you know which command to type for your version of Windows.
In Windows 7 and Windows Vista, type the following command at the Recovery Console prompt:
BOOTREC /FIXMBR
Type the command exactly as written: BOOTREC, a space, a forward slash, and then FIXMBR not followed by a period. Press Enter.
In Windows XP, you type the following command to fix the master boot record at the Recovery Console prompt:
FIXMBR
Press the Enter key and then press Y and Enter to confirm.
For all versions of Windows, this command works instantly. You see another command prompt displayed. Type exit to quit the command prompt. Restart the PC if it doesn’t restart automatically.
When the computer restarts, whatever problems afflicted the MBR should be gone. For example, if you were removing a boot manager program, it no longer appears when the PC first starts.
No danger is involved in fixing the MBR; if it wasn’t damaged, running the FIXMBR command doesn’t screw anything up (well, unless something else is wrong with the boot drive).
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