Dual-boot systems that boot whichever partition is marked Active are not affected by the fdisk /mbr command.įor more information about partitioning, query on the following word in the Microsoft Knowledge Base: The fdisk /mbr command erases this program. Some dual-boot programs have a special MBR that asks you at startup which operating system you want to use. Additional partition information is commonly stored information on partitions in an area that the fdisk /mbr command overwrites. Some older original equipment manufacturer (OEM) versions of MS-DOS and some third-party partitioning utilities can create more than four partitions. The fdisk /mbr command erases that information, making the disk unusable. The /bootall switch stores information about how the drive has been changed in an area of the master boot record that MS-DOS does not use. The Storage Dimensions SpeedStor utility with the /bootall option redefines the drive's physical parameters (cylinder, head, and sector). The disk was partitioned using the Storage Dimensions SpeedStor utility with its /bootall option. However, if Setup or Uninstal does not remove this message, or if the master boot record becomes corrupted, a new master boot record can be written to the disk using the following command:ĭo not use this command if any of the following conditions exists: If a problem occurs during Setup and you return to the previous version of MS-DOS, Uninstal should also remove this message. This message should be erased and the master boot code rewritten before Setup is completed. Insert the UNINSTALL #1 diskette in drive A. You cannot specify any other drive for the fdisk /mbr command to operate on other than DISK-0.ĭuring the installation of Microsoft MS-DOS Upgrade, Setup replaces the master boot record on the hard disk with code to display a message similar to: NOTE : The fdisk /mbr command only re-writes the MBR on the system drive (DISK-0) using BIOS calls. During typical operation, Fdisk writes this program to the disk only if there is no master boot record. This program is written to the disk by the fdisk /mbr command and is usually called the master boot record. This program uses the partition information to determine which partition is bootable (usually the first primary DOS partition) and attempts to boot from it. The partition information, or partition table, is stored at the end of this sector. There is a small program at the beginning of this sector of the hard disk. This first sector of the hard disk is called the master boot record (or sometimes the partition table or master boot block). It can also cause problems for some dual-boot programs and disks with more than four partitions.Īt the end of the ROM BIOS bootstrap routine, the BIOS reads and executes the first physical sector of the first floppy or hard disk on the system. WARNING : Writing the master boot record to the hard disk in this manner can make certain hard disks partitioned with SpeedStor unusable. Repartitioning with Fdisk does not rewrite this information.įdisk has an undocumented parameter called /mbr that causes it to write the master boot record to the hard disk without altering the partition table information. The MS-DOS Fdisk utility usually updates the master boot record (MBR) only if no master boot record exists.
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