What Is the Master Boot Code? (MBC Definition) GA S REGULAR Menu Lifewire Tech for Humans Newsletter! Search Close GO Software & Apps > Windows
What Is the Master Boot Code?
Definition of Master Boot Code & Help Fixing Master Boot Code Errors
By Tim Fisher Tim Fisher Senior Vice President & Group General Manager, Tech & Sustainability Emporia State University Tim Fisher has more than 30 years' of professional technology experience. He's been writing about tech for more than two decades and serves as the VP and General Manager of Lifewire. lifewire's editorial guidelines Updated on January 26, 2022 Tweet Share Email Tweet Share Email Windows The Ultimate Laptop Buying Guide The master boot code (sometimes abbreviated as MBC) is one of the several parts of the master boot record. It performs the first set of important functions in the process of booting. Specifically, in the typical generic master boot record, the master boot code consumes 446 bytes of the total 512-byte master boot record—the remaining space is used by the partition table (64 bytes) and the 2-byte disk signature. Anthony Bradshaw / Photographer's Choice / Getty Images How the Master Boot Code Works
Assuming the master boot code is executed properly by BIOS, the master boot code hands off booting control to the volume boot code, part of the volume boot sector, on the partition on the hard drive that contains the operating system. A master boot code is used only on primary partitions. Non-active partitions like those on an external drive that may store data like file backups, for example, don't need to be booted from because they don't contain an operating system and therefore have no reason for a master boot code. These are the actions the master boot code follows, according to Microsoft: Scans the partition table for the active partition. Finds the starting sector of the active partition. Loads a copy of the boot sector from the active partition into memory. Transfers control to the executable code in the boot sector. The master boot code uses what's called CHS fields (Starting and Ending Cylinder, Head, and Sector fields) from the partition table to locate the boot sector portion of the partition. Master Boot Code Errors
Files that Windows needs to boot to the operating system can sometimes become corrupt or go missing. Master boot code errors can happen due to anything from a virus attack that replaces the data with malicious codes, to physical damage to the hard drive. Identifying Master Boot Code Errors
One of these errors are likely displayed if the master boot code can't find the boot sector, preventing Windows from starting: Missing operating systemInvalid partition tableError loading operating systemMBR Error 1MBR Error 2 One way you can fix errors in the master boot record is to reinstall Windows. While this may be your first thought because you don't want to go through the process of fixing the error, it's a rather drastic solution. Let's look at a few other, potentially more simple, ways to fix these problems: How to Fix Master Boot Code Errors
While you can normally open a Command Prompt to run commands in Windows, problems with the master boot code likely mean that Windows won't start. In these cases, you'll need to access a Command Prompt from outside of Windows... In Windows 11, Windows 10, Windows 8, Windows 7, and Windows Vista, you can attempt to fix a master boot code error by rebuilding the Boot Configuration Data (BCD) using the bootrec command. The bootrec command can be run in Windows 11/10/8 through Advanced Startup Options. In Windows 7 and Windows Vista, you can run the same command, but it's done via System Recovery Options. In Windows XP and Windows 2000, the fixmbr command is used for building a new master boot record by re-writing the master boot code. This command is available in Recovery Console. Was this page helpful? Thanks for letting us know! Get the Latest Tech News Delivered Every Day Subscribe Tell us why! Other Not enough details Hard to understand Submit More from Lifewire Master Boot Record Definition (MBR, Sector Zero) Recovery Console: What It Is & a List of Commands Error Code 0xc00000e9: What It Means and How to Fix It Volume Boot Record Definition (Partition Boot Sector) What Is the Volume Boot Code (VBC Definition) How to Fix the 'Operating System Not Found' Error How to Use Bootsect /nt60 to Update the VBC to BOOTMGR How to Fix NTLDR Is Missing and Related NTLDR Errors Fixboot Command (Recovery Console) How to Write a New Partition Boot Sector for Windows XP 11 Best Free Disk Partition Software Tools (Oct. 2022) How to Fix Hal.dll Errors in Windows 11, 10, 8, 7 & Vista How to Rebuild the BCD in Windows How to Fix Missing Hal.dll Errors in Windows XP How to Repair the Master Boot Record In Windows XP What Is a Volume Serial Number? (VSN Definition) Newsletter Sign Up Newsletter Sign Up Newsletter Sign Up Newsletter Sign Up Newsletter Sign Up By clicking “Accept All Cookies”, you agree to the storing of cookies on your device to enhance site navigation, analyze site usage, and assist in our marketing efforts. Cookies Settings Accept All Cookies