KB102870 - Reading the Boot Sector of a Drive

Article ID: 102870

Article Last Modified on 8/30/2004

Microsoft Windows Software Development Kit 3.1

This article was previously published under Q102870

SUMMARY

BOOTSEC demonstrates how to use Interrupt 25h (absolute disk read) to read the boot sector (the first sector on head 0, cylinder 0) off of a drive (either a floppy disk drive or hard disk).

BOOTSEC checks to see whether the drive is one of the following:

   Drive            Detection Method
   ---------------------------------
   CD-ROM           Interrupt 2F calls to MSCDEX.
   Net drive        Windows API WNetGetConnection().
   RAM drive        Checks the boot sector to see if there is one FAT.
   Hard disk        Checks the media BYTE of the boot sector. If it is
                    equal to 0xF8h then it is a hard disk.
   Floppy disk      Checks the media BYTE of the boot sector. If it is
                    not equal to 0xF8h and it is not a RAM drive, net
                    drive, or CD-ROM drive, then it is a floppy disk drive.

BOOTSEC also shows how to implement a dialog box as a main window using a private dialog class.

MORE INFORMATION

The following files are available for download from the Microsoft Download Center:

Bootsec.exe

For additional information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base:

119591 How to Obtain Microsoft Support Files from Online Services

Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help to prevent any unauthorized changes to the file.

The following information is contained in the boot sector:

The jump instruction to the boot strap routine
The name of the OEM and the version of MS-DOS
Bytes per sector
Sectors per cluster
Reserved sectors
Number of file allocation tables
Number of root directory entries
Number of sectors
Media descriptor
Number of sectors occupied by each FAT
Number of sectors on a single track
Number of read/write heads on the drive
Number of hidden sectors
Number of huge sectors
Whether the disk is the first hard disk drive
The boot signature
The volume serial number
The volume label
The file system type

NOTE: The information contained in the boot sector was changed in MS-DOS 5.0. If this program is run on a disk that was formatted with a previous version of MS-DOS, then some of the fields in the structure will not be filled out, and the program may display garbage. The elements of the structure that were not changed will be displayed correctly.

Additional query words: INT softlib BOOTSEC.EXE KBFILE

Keywords: kb16bitonly kbfile kbsample KB102870