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Master Boot Record

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July 8, 2004 12:59:43 PM

Archived from groups: microsoft.public.windowsxp.hardware (More info?)

What is the difference between a Master Boot Record and
the Boot Sector

More about : master boot record

Anonymous
July 8, 2004 3:55:30 PM

Archived from groups: microsoft.public.windowsxp.hardware (More info?)

rick said in news:2915201c46504$95abb7f0$a501280a@phx.gbl:
> What is the difference between a Master Boot Record and
> the Boot Sector

The MBR is in the first sector on the physical disk first found by the BIOS in scanning for fixed disks. This sector is NOT included in any partition. The first 460 bytes of the MBR is the bootstrap program. The first 460 bytes are reserved for the bootstrap program but not all of may be used; most standard bootstrap programs are shorter (but boot managers may use it all and may even use the rest of the unused first track [which includes sector 0 for the MBR] to provide additional partitioning information and execution code). The standard bootstrap program (and not those used by boot managers that usurp the MBR) looks at the partition table (also within the MBR) to see which primary partition is marked as active and will load the boot code from that partition's boot sector (the first sector of that partition). When you run Windows XP's FIXMBR program (from the Recovery Console), it replaces the 460-byte bootstrap area in the MBR with a standard boot program.

The boot sector is the first sector of the *partition* containing the OS (or, at least, the first part of the OS used to start loading it). This contains the loader program to kick off the startup of the OS. When you run Windows XP's FIXBOOT program (from the Recovery Console), it overwrites the boot sector of the partition (assigned to the drive letter specified).

The BIOS loads the bootstrap program from the MBR of the first physically scanned fixed disk. This bootstrap program looks at the partition table which is also in the MBR to determine which primary partition is active (logical drives within extended partitions cannot be seen by the standard bootstrap program to use them for booting; only primary partitions can be used for booting). It then loads the boot code in the first sector of that active partition. Because the partition table in the MBR contains information regarding the partitions only on that physical drive, the bootstrap program can only load a boot sector from a partition on that same drive. Boot managers are not limited in this way. For NT-based versions of Windows, see http://support.microsoft.com/?id=100323; step 9 is where the boot sequence switches from using the "system partition" to using the "boot partition" (see below on how Microsoft reverses the naming of these partitions from what you and I would use for their description).

Once the bootstrap program (in the MBR) has loaded the boot code (in a partition's boot sector), it is possible the boot code can load the rest of the OS from a different physical drive. This is why the "system partition" for NT-based Windows is on the first physical hard drive but the "boot partition" for the rest of the OS can be in the same or different drive. Note that Microsoft uses terminology that is backwards from expected. To them, the "system partition" is where exists the boot sector and loader files to *boot* the OS, and this is where you find NTLDR, NTDETECT.COM, and boot.ini. The "boot partition" is where exists the rest of the *system* files that get loaded (kernel, GUI, etc.) and can be the same or different partition and/or drive as the "system partition". So the "system partition" is where the OS boot sector and loader files are found to boot the OS and the "boot partition" is where the rest of the system files are found. See http://support.microsoft.com/?id=314470 for Microsoft's description.

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Anonymous
July 8, 2004 6:42:49 PM

Archived from groups: microsoft.public.windowsxp.hardware (More info?)

I just have to say WOW. That was an excellent post. That is some neat
info you have there ;) 

Nathan McNulty

*Vanguard* wrote:

> rick said in news:2915201c46504$95abb7f0$a501280a@phx.gbl:
>
>>What is the difference between a Master Boot Record and
>>the Boot Sector
>
>
> The MBR is in the first sector on the physical disk first found by the BIOS in scanning for fixed disks. This sector is NOT included in any partition. The first 460 bytes of the MBR is the bootstrap program. The first 460 bytes are reserved for the bootstrap program but not all of may be used; most standard bootstrap programs are shorter (but boot managers may use it all and may even use the rest of the unused first track [which includes sector 0 for the MBR] to provide additional partitioning information and execution code). The standard bootstrap program (and not those used by boot managers that usurp the MBR) looks at the partition table (also within the MBR) to see which primary partition is marked as active and will load the boot code from that partition's boot sector (the first sector of that partition). When you run Windows XP's FIXMBR program (from the Recovery Console), it replaces the 460-byte bootstrap area in the MBR with a standard boot program.
>
> The boot sector is the first sector of the *partition* containing the OS (or, at least, the first part of the OS used to start loading it). This contains the loader program to kick off the startup of the OS. When you run Windows XP's FIXBOOT program (from the Recovery Console), it overwrites the boot sector of the partition (assigned to the drive letter specified).
>
> The BIOS loads the bootstrap program from the MBR of the first physically scanned fixed disk. This bootstrap program looks at the partition table which is also in the MBR to determine which primary partition is active (logical drives within extended partitions cannot be seen by the standard bootstrap program to use them for booting; only primary partitions can be used for booting). It then loads the boot code in the first sector of that active partition. Because the partition table in the MBR contains information regarding the partitions only on that physical drive, the bootstrap program can only load a boot sector from a partition on that same drive. Boot managers are not limited in this way. For NT-based versions of Windows, see http://support.microsoft.com/?id=100323; step 9 is where the boot sequence switches from using the "system partition" to using the "boot partition" (see below on how Microsoft reverses the naming of these partitions from what you and I would
use for their description).
>
> Once the bootstrap program (in the MBR) has loaded the boot code (in a partition's boot sector), it is possible the boot code can load the rest of the OS from a different physical drive. This is why the "system partition" for NT-based Windows is on the first physical hard drive but the "boot partition" for the rest of the OS can be in the same or different drive. Note that Microsoft uses terminology that is backwards from expected. To them, the "system partition" is where exists the boot sector and loader files to *boot* the OS, and this is where you find NTLDR, NTDETECT.COM, and boot.ini. The "boot partition" is where exists the rest of the *system* files that get loaded (kernel, GUI, etc.) and can be the same or different partition and/or drive as the "system partition". So the "system partition" is where the OS boot sector and loader files are found to boot the OS and the "boot partition" is where the rest of the system files are found. See http://support.microsof
t.com/?id=314470 for Microsoft's description.
>
!