Sunday, August 21, 2011

Rebuild Windows MBR with MiniTool Partition Wizard

MBR is short for Master Boot Record that is stored on cylinder0, head 0 and sector 1. MBR takes up 512 bytes comprising master boot program, Disk Partition Table and 55AA. MBR neither belongs to any operating system nor Windows operating systems. However, MBR which is vitally significant for a computer would result in computer boot failure when its content is changed. Though user could not read MBR content with Windows operating command, user can change or rewrite this area via command. Therefore, we may find the computer fails to boot when we restart computer after installing new software, this is results from the changes of MBR content performed by the newly installed software. To resolve this problem, user needs some third-party disk management tool to restore MBR functions. Here, I would like to recommend MiniTool Partition Wizard, a powerful partition manager developed by MiniTool Solution Ltd. with numerous functions including wipe partition, resize partition, merge partition, create partition, delete partition, format partition, convert partition format, copy partition.

Boot process of computer
Upon starting, a personal computer's x86 CPU runs the instruction located at the memory location CS:IP F000:FFF0 of the BIOS, which is located at the 0xFFFF0 address. This memory location is close to the end of the 1MB of system memory accessible in real mode. It typically contains a jump instruction that transfers execution to the location of the BIOS start-up program. This program runs a power-on self test to check and initialize required devices. The BIOS goes through a pre-configured list of non-volatile storage devices until it finds one that is bootable. A bootable device is defined as one that can be read from, and the last two bytes of the first sector contain the word 0xAA55.

A hex dump of FreeBSD's boot0 MBR
Once the BIOS has found a bootable device it loads the boot sector to hexadecimal Segment: Offset address 0000:7C00 or 07C0:0000 (maps to the same ultimate address) and transfers execution to the boot code. In the case of a hard disk, this is referred to as the master boot record (MBR) and is often not operating system specific. The conventional MBR code checks the MBR's partition table for a partition set as bootable (the one with active flag set). If an active partition is found, the MBR code loads the boot sector code from that partition and executes it. The boot sector is often operating-system-specific; however, in most operating systems its main function is to load and execute the operating system kernel, which continues startup. If there is no active partition, or the active partition's boot sector is invalid, the MBR may load a secondary boot loader which will select a partition and load its boot sector, which usually loads the corresponding operating system kernel.

Some systems use Intel's proprietary EFI. Also coreboot allows a computer to boot without having an over-complicated firmware/BIOS constantly running in system management mode. The legacy 16-bit BIOS interfaces are required by certain x86 operating systems, such as Windows. However most boot loaders have 16-bit support for these legacy BIOS systems.

Restore MBR with MiniTool Partition Wizard
User should first download MiniTool Partition Wizard at MiniTool Partition Wizard Download Center and then install it to computer.

User would meet following interface after running MiniTool Partition Wizard. Select and right click the disk to be rebuilt and then click "Rebuild MBR".

Lastly, click "Apply" in this main interface to execute pending operation, rebuilding MBR successfully.

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