This index lists all INT 21H functions, organized by function number,
and identifying the DOS versions under which they are available.

See DOS Function Index - by DOS Version to see functions in the
chronological order in which they were added to DOS.
See DOS Function Index - Quick Reference Subset for a one-screen summary.

Versions  DOS Function
 1.0+   00H   Terminate a Program
 1.0+   01H   Keyboard Input
 1.0+   02H   Display Output
 1.0+   03H   Auxiliary Input
 1.0+   04H   Auxiliary Output
 1.0+   05H   Printer Output
 1.0+   06H   Console I/O
 1.0+   07H   No Echo Unfiltered Console Input
 1.0+   08H   No Echo Console Input
 1.0+   09H   Display String
 1.0+   0aH   Buffered String Input
 1.0+   0bH   Check Input Status
 1.0+   0cH   Clear & Input
 1.0+   0dH   Reset Disk
 1.0+   0eH   Select DOS Default Disk
 1.0+   0fH   Open File via FCB
 1.0+   10H   Close File via FCB
 1.0+   11H   Find 1st Matching File via FCB
 1.0+   12H   Find Next Matching File via FCB
 1.0+   13H   Delete File via FCB
 1.0+   14H   Read Sequential File via FCB
 1.0+   15H   Write Sequential File via FCB
 1.0+   16H   Create File via FCB
 1.0+   17H   Rename File via FCB
 ?.?    18H   (unknown)                                          obsolete 
 1.0+   19H   Query DOS Default Disk
 1.0+   1aH   Set Disk Transfer Address (DTA)
 1.0+   1bH   Get Drive Info (current disk)
 2.0+   1cH   Get Drive Info (any disk)
 ?.?    1dH   (unknown)                                          obsolete 
 ?.?    1eH   (unknown)                                          obsolete 
 2.0+   1fH   Get Drive Parameter Block (current disk)           wasUndoc 
 ?.?    20H   (unknown)                                          obsolete 
 1.0+   21H   Read Random File Record
 1.0+   22H   Write Random File Record
 1.0+   23H   Query File Size via FCB
 1.0+   24H   Set Random File Block Address
 1.0+   25H   Set Interrupt Vector
 1.0+   26H   Create Program Segment Prefix
 1.0+   27H   Read Random File Block
 1.0+   28H   Write Random File Block
 1.0+   29H   Parse Filename
 1.0+   2aH   Query DOS Date
 1.0+   2bH   Set DOS Date
 1.0+   2cH   Query DOS Time
 1.0+   2dH   Set DOS Time
 1.0+   2eH   Set/Reset Verify Switch
 2.0+   2fH   Query Disk Transfer Address (DTA)
 2.0+   30H   Get DOS Version Number
 2.0+   31H   Terminate & Stay Resident
 2.0+   32H   Get DPB (Drive Parameter Block)                    wasUndoc 
 2.0+   3300H Query Break-Check Flag
 2.0+   3301H Set Break-check level
 2.0+   3305H Get Boot Drive                                     wasUndoc 
 5.0+   3306H Get DOS Version Info (and HMA use)
 2.0+   34H   Get InDOS Address (DOS Reentrancy Status)          wasUndoc 
 2.0+   35H   Get Interrupt Vector
 2.0+   36H   Get Disk Free Space
 ?.?    3700H Query Switchar                                     obsolete 
 ?.?    3701H Set Switchar                                       obsolete 
 2.0+   38H   Get/Set Country-dependent Info
 2.0+   39H   Create a New Directory -- MKDIR
 2.0+   3aH   Delete a Directory -- RMDIR
 2.0+   3bH   Set DOS Default Directory -- CHDIR
 2.0+   3cH   Create a File via Handle
 2.0+   3dH   Open a File via Handle
 2.0+   3eH   Close a File Handle
 2.0+   3fH   Read from File via Handle
 2.0+   40H   Write to File via Handle
 2.0+   41H   Delete File
 2.0+   42H   Set File Pointer
 2.0+   4300H Query File Attribute
 2.0+   4301H Set File Attribute
 2.0+   4400H IOCTL Query Device/File Flags
 2.0+   4401H IOCTL Set Device/File Flags
 2.0+   4402H IOCTL Receive Control Data from Char Device
 2.0+   4403H IOCTL Send Control Data to Character Device
 2.0+   4404H IOCTL Receive Control Data from Block Device
 2.0+   4405H IOCTL Send Control Data to Block Device
 2.0+   4406H IOCTL Query Handle Input Status
 2.0+   4407H IOCTL Query Handle Output Status
 3.0+   4408H IOCTL Does Drive Use Removable Media
 3.1+   4409H IOCTL Is Drive Remote
 3.1+   440aH IOCTL Is File/Device Remote
 3.1+   440bH IOCTL Set Sharing Retry Count
 3.3+   440cH 45H IOCTL Set Retry Iteration Count
 3.3+   440cH 4AH IOCTL Select Code Page
 3.3+   440cH 4CH IOCTL Start Code Page Prepare
 3.3+   440cH 4DH IOCTL End Code Page Prepare
 4.0+   440cH 5Fh IOCTL Set Display Mode
 3.3+   440cH 65H IOCTL Query Retry Iteration Count
 3.3+   440cH 6AH IOCTL Query Current Code Page
 3.3+   440cH 6BH IOCTL Query Code Page List
 4.0+   440cH 7Fh IOCTL Query Display Mode
 3.2+   440dH 40H IOCTL Set Device Parameters
 3.2+   440dH 41H IOCTL Write Track on Logical Drive
 3.2+   440dH 42H IOCTL Format Track on Logical Drive
 4.0+   440dH 46H IOCTL Set Media ID
 3.2+   440dH 47H IOCTL Set Access Flag
 3.2+   440dH 60H IOCTL Query Device Parameters
 3.2+   440dH 61H IOCTL Read Track on Logical Drive
 3.2+   440dH 62H IOCTL Verify Track on Logical Drive
 5.0+   440dH 66H IOCTL Query Media ID
 4.0    440dH 67H IOCTL Query Access Flag
 3.2+   440dH 68H IOCTL Sense Media Type
 3.2+   440eH IOCTL Query Logical Drive Map
 3.2+   440fH IOCTL Set Logical Drive Map
 5.0+   4410H IOCTL Query IOCTL Support for Handle
 5.0+   4411H IOCTL Query IOCTL Support for Device
 2.0+   45H   Duplicate a File Handle
 2.0+   46H   Redirect a Handle
 2.0+   47H   Query Default Directory
 2.0+   48H   Allocate Memory / Query Free Memory
 2.0+   49H   Free Allocated Memory Block
 2.0+   4aH   Shrink or Expand a Memory Block
 2.0+   4b00H Execute a Program -- EXEC
 2.0+   4b01H Load Program                                       wasUndoc 
 2.0+   4b03H Load Overlay
 5.0+   4b05H Set Execution State
 2.0+   4cH   Terminate Program
 2.0+   4dH   Get Program Exit Code
 2.0+   4eH   Find 1st Matching File
 2.0+   4fH   Find Next Matching File
 2.0+   50H   Set PSP                                            wasUndoc 
 2.0+   51H   Query Current PSP                                  wasUndoc 
 ????   52H   Get DOS Variables                                     undoc 
 ????   53H   Convert BPB to DPB                                    undoc 
 2.0+   54H   Get DOS Verify State
 2.0+   56H   Rename/Move a File
 2.0+   5700H Query File Time/Date
 2.0+   5701H Set File Time/Date
 3.0+   5800H Query Memory Allocation Strategy
 3.0+   5801H Set Memory Allocation Strategy
 5.0+   5802H Query Upper-Memory Link State
 5.0+   5803H Set Upper-Memory Link State
 3.0+   59H   Get Extended Error Info
 3.0+   5aH   Create Unique Temporary File
 3.0+   5bH   Create New File
 3.1+   5c00H Lock File Access
 3.1+   5c01H Unlock File Access
 4.0+   5d0aH Set Extended Error
 3.1+   5e00H Query Network Node Name
 3.1+   5e02H Set Network Printer Setup
 3.1+   5e03H Query Network Printer Setup
 3.1+   5f02H Network Query Assign-List Entry
 3.1+   5f03H Make Network Connection
 3.1+   5f04H Delete Network Connection
 ????   60H   Query TrueName                                        undoc 
 2.0+   62H   Query Current PSP                                  wasUndoc 
 3.3+   6501H Get Extended Country Information
 3.3+   6504H Get Uppercase Table
 3.3+   6505H Get Filename Character Table
 3.3+   6506H Get Collating Sequence Table
 3.3+   6507H Get Double-Byte Character Set
 3.3+   6520H Upshift Character
 3.3+   6521H Upshift String
 3.3+   6522H Upshift ASCIIZ String
 3.3+   6601H Query Active Code Page
 3.3+   6602H Activate Code Page
 3.3+   67H   Set File Handle Count
 3.3+   68H   Commit File
 4.0+   6cH   Extended Open/Create
DOS Versions (summary of differences from version to version)
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DOS Function Index - by Number