Click above to get retro games delivered to your door ever month!

  All DOS function calls described in this chapter are invoked through
  interrupt 21H (decimal 33). The individual functions are selected by
  placing the function number in the AH register. Any program that uses
  these functions should test the DOS version number first to be sure the
  functions are supported. (Function 30H provides this service.)

  The functions can be organized into the groups shown in Figure 17-2. In
  an effort to make the logical groupings of the function calls as clear as
  possible, we organized and described them in a slightly different manner
  than that in IBM's DOS technical reference manuals. You may want to
  compare this organization with IBM's, to be sure you understand. Figure
  17-3 lists the individual function calls.

        Function
  Hex            Dec            Group
  --------------------------------------------------------------------------
  2FH-38H        47-56          Miscellaneous functions
  39H-3BH        57-59          Directory functions
  3CH-46H        60-70          File-management functions
  47H            71             Directory function
  48H-4BH        72-75          Memory-management functions
  4CH-5BH        76-91          Miscellaneous functions
  5CH-5FH        92-95          Network support
  62H-68H        98-104         Miscellaneous functions
  --------------------------------------------------------------------------

  Figure 17-2.  The logical groups of extended DOS function calls.


   Function                                                  DOS
  Hex    Dec     Description                                 Version
  --------------------------------------------------------------------------
  2FH    47      Get DTA Address                            2.0
  30H    48      Get DOS Version Number                     2.0
  31H    49      Terminate and Stay Resident                2.0
  33H    51      Get/Set Ctrl-C Flag                        2.0
  35H    53      Get Interrupt Vector                       2.0
  36H    54      Get Disk Free Space                        2.0
  38H    56      Get/Set Country-Dependent Information      2.0
  39H    57      Create Directory                           2.0
  3AH    58      Remove Directory                           2.0
  3BH    59      Change Current Directory                   2.0
  3CH    60      Create File                                2.0
  3DH    61      Open Handle                                2.0
  3EH    62      Close Handle                               2.0
  3FH    63      Read from File or Device                   2.0
  40H    64      Write to File or Device                    2.0
  41H    65      Delete File                                2.0
  42H    66      Move File Pointer                          2.0
  43H    67      Get/Set File Attributes                    2.0
  44H    68      IOCTL--I/O Control for Devices             2.0
  45H    69      Duplicate File Handle                      2.0
  46H    70      Force Duplicate File Handle                2.0
  47H    71      Get Current Directory                      2.0
  48H    72      Allocate Memory Block                      2.0
  49H    73      Free Memory Block                          2.0
  4AH    74      Resize Memory Block                        2.0
  4BH    75      EXEC--Load and Execute a Program           2.0
  4CH    76      Terminate with Return Code                 2.0
  4DH    77      Get Return Code                            2.0
  4EH    78      Find First Matching Directory Entry        2.0
  4FH    79      Find Next Matching Directory Entry         2.0
  54H    84      Get Verify Flag                            2.0
  56H    86      Rename File                                2.0
  57H    87      Get/Set File Date and Time                 2.0
  58H    88      Get/Set Memory Allocation Strategy         3.0
  59H    89      Get Extended Error Information             3.0
  5AH    90      Create Temporary File                      3.0
  5BH    91      Create New File                            3.0
  5CH    92      Lock/Unlock File Region                    3.0
  5EH    94      Network Machine Name and Printer Setup     3.1
  5FH    95      Network Redirection                        3.1
  62H    98      Get PSP Address                            3.0
  65H    101     Get Extended Country Information           3.3
  66H    102     Get/Set Global Code Page                   3.3
  67H    103     Set Handle Count                           3.3
  68H    104     Commit File                                3.3
  --------------------------------------------------------------------------


  Figure 17-3.  Interrupt 21H functions available in DOS versions 2.0 and
  later.