Reading the Boot Sector of a Drive

ID: Q102870

The information in this article applies to:

Microsoft Windows Software Development Kit (SDK) 3.1

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. Click the file names below to download the files:

Bootsec.exe

For more information about how to download files from the Microsoft Download Center, please visit the Download Center at the following Web address

http://www.microsoft.com/downloads/search.asp

and then click How to use the Microsoft Download Center.

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 : kbfile kbsample kb16bitonly kbWinOS310 KrFileIO
Version : WINDOWS:3.1
Platform : WINDOWS
Issue type :