DEBUG Script to Clear Partition Sector of Hard Drive

Filename: HDCLEAR.TXT
WWW URL:  http://www.firmware.com/support/bios/hdclear.htm
FTP URL:  ftp://ftp.firmware.com/text/hdclear.txt
Revision: 02/11/99  TLS  Micro Firmware Technical Support
Summary:  This DEBUG script is used to erase a hard drive when other
          methods are not sufficient.

Even if you have repartitioned the hard drive, FDISK does not update the entire partition sector after the first time. The following DEBUG script will clear the partition sector (cyl 0, head 0, sector 1) of the first hard drive, which will force FDISK to completely start over. This is sometimes useful for removing Disk Manager or EZ Drive and should also remove any boot sector viruses, providing that the virus is not active in memory, which should be the case if you have booted clean from a non-infected diskette. Although this script clears only the first physical drive, we recommend unplugging other drives to prevent accidental data loss. Letters in script are not case-sensitive.

      A:\>DEBUG

      - f 200 L200 0

      - a 100                

      xxxx:0100  mov ax,301   (ignore segment:offset values at left)

      xxxx:0103  mov bx,200

      xxxx:0106  mov cx,1

      xxxx:0109  mov dx,0080

      xxxx:010C  int 13

      xxxx:010E  int 3

      xxxx:010F               (Press ENTER an extra time here)

      - d 100 LF

      xxxx:0100 B8 01 03 BB 00 02 B9 01-00 BA 80 00 CD 13 CC

      (make sure that hex values match above line before proceeding)

      (if values do not match, type Q and start over)

      - g=100

                              (ignore register display)

      - q                     (quits back to DOS)

 - f 200 L200 0  FILL Length of 512 bytes at offset 200 with value 0
 - a 100         ASSEMBLE program at offset 100

      (Next 4 lines set up registers for INT13 - Function 03)

   mov ax,301    AH=03 INT13 function 03 - Write Disk Sectors

                 AL=01 specifies how many sectors to write (1)

   mov bx,200    BH=02 BL=00 points to buffer area at offset 200

   mov cx,1      CH=00 specifies cylinder 0 for INT13 function 03 

                 CL=01 specifies sector 1 (first sector on drive)

   mov dx,0080   DH=00 specifies head 0 (first head on drive)

                 DL=80 specifies physical fixed disk drive 1

                    (81=2nd drive, 82=3rd drive, 83=4th drive)

   int 13        call INT13 (BIOS Fixed Disk Device Service Routine)

   int 3         return to DEBUG (after assembling program)
 - d 100 LF      this line is optional - the resulting hex dump can be

                 used as a check to verify that instructions have been

                 entered correctly
 - g=100         GO - run program stored at offset 100
 - q             QUIT DEBUG back to DOS prompt