re-writing number of series using C?

Posted on 1999-01-05
Last Modified: 2010-04-15
hi experts!

  I use Borland C 3.1 and I need change the number of series of my 3.5" microdisk(disquettes).  (what interruption is and what service?)

What can I do??
(please write me a small sample skeletor source code )

Thanks again for all!
Question by:nowait
  • 4
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LVL 11

Accepted Solution

alexo earned 150 total points
ID: 1255565
Quoting from MS KB article Q69223:

The information in this article applies to:
 - The C Run-time (CRT) included with:
    - Microsoft C for MS-DOS, versions 5.1, 6.0, 6.0a, and 6.0ax
    - Microsoft C/C++ for MS-DOS, version 7.0
    - Microsoft Visual C++ for Windows, versions 1.0 and 1.5
Beginning with MS-DOS version 4.0, a semi-random 32-bit binary
identification number (ID) is assigned to each disk that MS-DOS
formats. The volume serial number (or ID) is stored at offset 27H to
2AH in the boot sector of each disk.
NOTE: code compiled with Visual C++ version 1.5 may yield the following
message from Windows NT:
   An applicaion has attempted to directly access the hard disk, which
   cannot be supported. This may cause the application to function
It provides Terminate and Ignore buttons. If the user is logged on with
Administrative privileges, this will succeed for a FAT partition, else it
fails for a FAT partition. It always fails for an NTFS partition. After
clicking Terminate or Ignore the program returns with the error message
that has been coded (error on int 25).
The following program illustrates how to retrieve this information:
/*                                                             */
/* This program reads the volume serial number (or ID) from    */
/* the boot sector of a specified disk. The DOS interrupt 25   */
/* Absolute Disk Read is used to read in the boot sector.      */
/*                                                             */
/* Note: The volume ID is only implemented from MS-DOS 4.0     */
/*       and later.                                            */
/*                                                             */
/* The output consists of the OEM name and version of the      */
/* disk-formatting program (stored at offset 03H to 0AH in the */
/* boot sector), the disk volume label, and the disk-volume    */
/* serial number.                                              */
/*                                                             */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <dos.h>
#include <conio.h>
char bootsector[1024];
char volume[12];
char ver[9];
char block[10];
void main(void)
   int ax, _far *p, drive;
   struct find_t fileinfo;
   char filename[13], _far *myvar, _far *q;
   union REGS inregs, outregs;
   struct SREGS segregs;
   printf("Enter drive number (0=A,1=B,2=C, ...): ");
   drive = getche() - '0';
   /* Parameter block for int 25H        */
   /* Bytes    Description               */
   /* -------  -----------               */
   /* 00H-03H  32-bit sector number      */
   /* 04H-05H  Number of sectors to read */
   /* 06H-07H  Offset of buffer          */
   /* 08H-09H  Segment of buffer         */
   block[0] = block[1] = block[2] = block[3] = 0;
   block[4] = 1;
   block[5] = 0;
   myvar = bootsector;
   p = (int *)&block[6];
   *p = FP_OFF(myvar);
   p = (int *)&block[8];
   *p = FP_SEG(myvar);
   q = block; = (char)drive; = -1;
   inregs.x.bx = FP_OFF(q);
   segregs.ds = FP_SEG(q);
   ax = int86x(0x25, &inregs, &outregs, &segregs);
   /*** Error routine ***/
   if (outregs.x.cflag)
      printf("\n\nerror on int 25\n");
      printf("this is AX:%04X", ax);
   /*** Output ***/
   printf("\n\nDrive %c\n-------\n\n", drive +'A');
   strncpy(ver, &bootsector[3], 8);
   printf("OEM name and version: %s\n", ver);
   /* Use _dos_findfirst for the volume label */
   filename[0] = (char)(drive + 'A');
   filename[1] = '\0';
   strcat(filename, ":\\*.*");
   if(!_dos_findfirst(filename, _A_VOLID, &fileinfo))
   printf("Volume name         : %s\n",;
   /* Before printing serial number, check if version >= 4.x */
   if ((ver[6] == '.') && (ver[5] >= '4') && (ver[5] <= '9'))
      printf("Serial number       : %02X%02X-%02X%02X\n\n",
                              (unsigned char) bootsector[0x2a],
                              (unsigned char) bootsector[0x29],
                              (unsigned char) bootsector[0x28],
                              (unsigned char) bootsector[0x27]);


Author Comment

ID: 1255566

excellent answer!!
Thanks Alexo!!
LVL 11

Expert Comment

ID: 1255567
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Author Comment

ID: 1255568
thanks again!!!!

Author Comment

ID: 1255569
thanks alexo!!!! but your sorce code read the serial number but I need write a NEW serial number !!

What can I do? Please alexo!!
thanks again!
LVL 11

Expert Comment

ID: 1255570
Well, INT 25h reads from the disk and INT 26h writes to the disk so after reading the boot sector, just change the 4 bytes at offset 0x27 and up and write them again.

One more thing, there are functions that are easier to use than int86x().  Here are some options:

1. Read the boot sector with absread() and write it with abswrite().
2. Use biosdisk().  Command 2 to read and command 3 to write.

The first option implicitly uses INT 25h and INT26h, the second uses INT 13h.

Author Comment

ID: 1255571
Thanks Again Alexo!!

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