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                             Detecting ANSI.SYS

        Compare segment address of a DOS interrupt with the segment of the
        standard CON device.  If equal, then ANSI is not loaded.  If the
        segment address of CON is greater than the DOS interrupt, then ANSI
        is loaded or a TSR is handling the interrupt.

        - see INT 21,52 for info on CON device address


                             Detecting DESQView

        1.  call INT 2F with AX = DE00h
        2.  if AL = FF on return DESQView is installed


                            Detecting Disk Ready

        1.  use INT 13,4 (Verify Sector) to check ready for read
        2.  check for error in AH of:
            80h  Time out, or Not Ready
            AAh  Drive not ready
            00h  drive is ready for reading
            other value indicates drive is ready, but an error occurred
        3.  use INT 13,2 (Read Sector) followed by INT 13,3 (Write Sector)
            to check ready for read/write.  First read sector, test for
            ready;  write sector back, check for 03h (write protect) or
            any of the other BIOS disk errors

        - multiple attempts should be made to allow for diskette motor startup
        - allows testing of drive ready by bypassing DOS and critical errors
        - see  INT 13,STATUS


                         Detecting Drive Existence

        1.  save current drive  (INT 21,19)
        2.  set current drive  (INT 21,E)
        3.  get current drive  (INT 21,19)
        4.  if current drive == drive requested
               then drive exists
               else drive doesn't exist
        5.  reset original drive  (INT 21,E)

        - no critical error is generated if invalid drive is selected


                            Detecting EGA Video

        INT 10h, function 12h (INT 10,12), subfunction 10h (in BL) will
        return BL = 10h if not an EGA since invalid functions requests
        return without register modification


                            Detecting VGA Video

        INT 10,1A can be used to detect the presence of VGA.
        BL = 7  VGA with analog monochrome display
           = 8  VGA with analog color display

        - some enhanced EGA adapters will incorrectly identify as VGA
          when INT 10,1B is used


                      Detecting Extended Keyboard BIOS

        1.  use INT 16,5 to stuff FFFF into the keyboard buffer
        2.  use INT 16,10 to read the keystrokes back
        3.  if the data stuffed into the keyboard is returned within 16
            extended reads, the BIOS handles the extended keyboard
        4.  byte at 40:96 (BDA) is another method of detecting extended BIOS
            but is not reliable since some compatibles give false positives

        - see   BIOS DATA AREA   INT 9


                Detecting present of Expanded Memory Manager

        1.  attempt to open file/device 'EMMXXXX0' using INT 21,3D;
            if successful continue, else no EMM
        2.  make sure EMMXXXX0 is a character device and not a disk file
            by using IOCTL function 0 (Get Device Info);  bit 7 of DX
            should be set for char device and clear for disk file
        3.  make sure Expanded Memory Manager is available using IOCTL
            function 7 (Get Output Status);  AL should be non-zero (FF)
            if Memory Manager is available, and zero if not available.
        4.  call INT 67,46  to get version information

        - see also   IOCTL,0   IOCTL,7


                    Detecting Existence of Mouse Driver

        1.  check INT 33 vector is not 0:0
        2.  check INT 33 vector does not point to an IRET
        3.  call INT 33,0 to reset the mouse and get installed state
        4.  call INT 33,24 to check version, type and IRQ


                          Detecting Miscellaneous

        Boot drive;   see INT 21,33 (DOS 4.0+)

        CPU type;   see CPU

        Hardware configuration;   see INT 11

        Logical Drive Assignment;   see IOCTL,E

        Memory size, Base;   see INT 12

        Memory size, Extended;   see CMOS

        Micro Channel Bus on PS/2;   see INT 15,C0

        Network or Local Disk;   see IOCTL,9

        Network or Local File;   see IOCTL,A

        Parallel ports;   see  BIOS DATA AREA  locations 40:08-40:0F

        RAM Disk;   see  INT 21,32   and   MEDIA DESCRIPTOR

        Redirection on command line;   see  IOCTL,0

        Removable media;   INT 21,1B  INT 21,1C
                           MEDIA DESCRIPTOR BYTE  and  IOCTL,8

        Serial ports;   see BIOS DATA AREA  locations 40:00-40:07

        Single drive A: or B: selection;   see BIOS DATA AREA byte 50:04

        SUBST'ed drive;  see INT 21,32

        Video Screen Size in Columns;  see  INT 10,F

        Video Screen Size in Rows;  see  INT 10,11  subfunction 30h (EGA+)

        APPEND resident;   see INT 2F,0
        ASSIGN resident;   see INT 2F,0
        DOSSHELL resident;   see INT 2F,0
        NLSFUNC resident;   see INT 2F,0
        PRINT resident;   see INT 2F,0
        SHARE resident;   see INT 2F,0