BIOS Equipment-List Word (61806)


The information in this article applies to:

  • Microsoft MS-DOS operating system 3.1
  • Microsoft MS-DOS operating system 3.2
  • Microsoft MS-DOS operating system 3.21
  • Microsoft MS-DOS operating system 3.3
  • Microsoft MS-DOS operating system 3.3a
  • Microsoft MS-DOS operating system 4.0
  • Microsoft MS-DOS operating system 4.01
  • Microsoft MS-DOS operating system 5.0
  • Microsoft MS-DOS operating system 5.0a
  • Microsoft MS-DOS operating system 6.0
  • Microsoft MS-DOS operating system 6.2
  • Microsoft MS-DOS operating system 6.21
  • Microsoft MS-DOS operating system 6.22
This article was previously published under Q61806

SUMMARY

This article describes a quick way to determine how many floppy disk drives, serial ports, and parallel ports are connected to the machine on which your software is running.

MORE INFORMATION

During the boot process, the ROM BIOS examines the computer's various connectors and sets an equipment-list word accordingly. This word is located at absolute address 410 hex or segment 0000, offset 0410 (hex). Interrupt 11 hex returns the word in the AX register. The bits of the word are defined as follows: 
   Bit       Description
   ---------------------

   0         Set if any floppy disk drives present

   1         Set if math coprocessor installed

   2         Set if pointing device attached (PS/2)

   3-2       System board RAM size (only for original IBM PC, PCjr):

                 00 = 16K
                 01 = 32K
                 10 = 48K
                 11 = 64K

   5-4        Initial video mode:

                 00 = reserved
                 01 = 40-column color
                 10 = 80-column color
                 11 = 80-column monochrome

   7-6        Number of floppy disk drives (if bit 0 set):

                 00 = 1 drive
                 01 = 2 drives
                 10 = 3 drives
                 11 = 4 drives

   8         Reserved

   11-9      Number of serial ports

   12        Set if game adapter installed

   13        Set if serial printer attached (PCjr)
             Set it internal modem installed (PC and XT only)

   15-14     Number of parallel ports
Modification Type:MajorLast Reviewed:5/12/2003
Keywords:KB61806
©2002 Microsoft Corporation. All rights reserved.