Clearing the Master Boot Record

 

This procedure goes 7 layers deep so no data will be recoverable. It goes far beyond  fdisk /mbr in clearing the master boot record. This will also remove an NTFS partion.

 

Use This Routine When:

1.     FDISK docs not recognize the hard disk and NO hard disk error messages appear on POST such as "FIXED DISK 0 FAILURE".

2.     There is a virus on the master boot record of the hard drive (in this case a DOS format will not remove the virus). This particularly applies when virus detection programs cannot eradicate the virus. A cold boot is necessary this is done to clear the virus from memory and prevent it from writing to the disk.  Follow this with a FORMAT C:/S/U.

3.     There are non-DOS partitions to be removed. This is will remove all partitions on the hard drive including any existing DOS, HPFS or NTFS partitions.

     

Using Debug

       l. Open an MS-DOS Command prompt.

       2. Type DEBUG and press Enter.

 

What to Type:

Display on Screen

Explanation

FCS:200 400 0  <ENTER>

 

Prepares a 400(hex) byte buffer filled with Os at ME offset 600(hex) that will be written to the appropriate
sector.
                             

RAX <ENTER>

AX 0000

Command to change the contents of the A,X register.

0301 <ENTER>

 

03=Write function, 0 l=Sector count, to clear sector 2 which contains the multimedia password/script for Windows 3.X system at the same time as the boot record. Enter 0302.
                             

RBX <ENTER>

BX 0000

Command to change the contents of the B,X register.

0600 <ENTER>

              

0600=Pointer to offset of the data that will be written to the sector(s).

RCX <ENTER>

CX 0000

Command to change the contents of the C,X register.

0001 <ENTER> 

 

000 l=Which sector to begin writing at. To clear just the multimedia password/script enter 0002.                     

RDX <ENTER>

DX 0000

Command to change the contents of the D,X register.

0080 <ENTER>

              

00=Head number, 80=drive type is fixed disk use 81when using this routine on a second hard drive.                                

E 100 CD 13 <ENTER>                      

 

Writes the assembly command to execute INT 13 to
memory offset 0100.

P <ENTER>

 

Executes the first assembly command at default memory                offset of 0100.                  

Q <ENTER>

 

Closes the debug program.