INT 21h (00h)      - PROGRAM TERMINATION
INT 21h (01h)      - KEYBOARD INPUT
INT 21h (02h)      - DISPLAY OUTPUT
INT 21h (03h)      - AUX Input
INT 21h (04h)      - AUX Output
INT 21h (05h)      - PRINTER OUTPUT
INT 21h (06h)      - DIRECT CONSOLE I/O - CHARACTER OUTPUT
INT 21h (06h)      - DIRECT CONSOLE I/O - CHARACTER INPUT
INT 21h (07h)      - Direct STDIN Input, no echo
INT 21h (08h)      - KEYBOARD INPUT - NO ECHO
INT 21h (09h)      - PRINT STRING
INT 21h (0Ah)      - BUFFERED KEYBOARD INPUT
INT 21h (0Bh)      - CHECK STANDARD INPUT STATUS
INT 21h (0Ch)      - Clear Keyboard Buffer
INT 21h (0Dh)      - Disk Reset
INT 21h (0Eh)      - SELECT DISK
INT 21h (0Fh)      - OPEN DISK FILE
INT 21h (10h)      - CLOSE DISK FILE
INT 21h (11h)      - Search First using FCB
INT 21h (12h)      - Search Next using FCB
INT 21h (13h)      - Delete File via FCB
INT 21h (14h)      - SEQUENTIAL DISK FILE READ
INT 21h (15h)      - SEQUENTIAL DISK RECORD WRITE
INT 21h (16h)      - CREATE A DISK FILE
INT 21h (17h)      - Rename File via FCB
INT 21h (18h)      - Internal - does nothing
INT 21h (19h)      - Default Disk Number
INT 21h (1Ah)      - SET DISK TRANSFER AREA ADDRESS
INT 21h (1Bh)      - Default Drive Disk Size
INT 21h (1Ch)      - Specific Drive's Disk Size
INT 21h (1Dh)      - Internal - does nothing
INT 21h (1Eh)      - Internal - does nothing
INT 21h (1Fh)      - Internal - GET DEFAULT DRIVE PARAMETER BLOCK
INT 21h (20h)      - Internal - does nothing
INT 21h (21h)      - RANDOM DISK RECORD READ
INT 21h (22h)      - Random Disk Write
INT 21h (23h)      - FILE SIZE
INT 21h (24h)      - Set Random Record Field
INT 21h (25h)      - Set Interrupt Vector
INT 21h (26h)      - Create PSP
INT 21h (27h)      - RANDOM BLOCK READ
INT 21h (28h)      - RANDOM BLOCK WRITE
INT 21h (29h)      - Parse Filename
INT 21h (2Ah)      - GET CURRENT DATE
INT 21h (2Bh)      - Set CURRENT DATE
INT 21h (2Ch)      - GET CURRENT TIME
INT 21h (2Dh)      - Set CURRENT TIME
INT 21h (2Eh)      - Set Verify Flag
INT 21h (2Fh)      - Get Disk Transfer Area Address
INT 21h (30h)      - Get DOS Version
INT 21h (31h)      - TERMINATE BUT STAY RESIDENT
INT 21h (32h)      - Internal - GET DRIVE PARAMETER BLOCK
INT 21h (33h)      - Get or Set CONTROL-BREAK
INT 21h (34h)      - Internal - Return CritSectFlag Pointer
INT 21h (35h)      - Get Interrupt Vector
INT 21h (36h)      - DISK SPACE
INT 21h (37h)      - Internal - switchar/availdev
INT 21h (38h)      - Get Country-Dependent Information
INT 21h (39h)      - CREATE A SUBDIRECTORY (MKDIR)
INT 21h (3Ah)      - REMOVE A DIRECTORY ENTRY (RMDIR)
INT 21h (3Bh)      - CHANGE THE CURRENT DIRECTORY (CHDIR)
INT 21h (3Ch)      - CREATE A FILE WITH HANDLE (CREAT)
INT 21h (3Dh)      - OPEN DISK FILE WITH HANDLE
INT 21h (3Eh)      - CLOSE A FILE WITH HANDLE
INT 21h (3Fh)      - READ FROM FILE WITH HANDLE
INT 21h (40h)      - WRITE TO FILE WITH HANDLE
INT 21h (41h)      - DELETE A FILE (UNLINK)
INT 21h (42h)      - MOVE FILE READ/WRITE POINTER (LSEEK)
INT 21h (43h)      - GET/PUT FILE ATTRIBUTES (CHMOD)
INT 21h (44h)      - IOCTL
INT 21h (45h)      - Create Duplicate Handle (DUP)
INT 21h (46h)      - Force Duplicate Handle (FORCDUP) (DUP2)
INT 21h (47h)      - Get Current Directory
INT 21h (48h)      - Allocate Memory
INT 21h (49h)      - Free Memory
INT 21h (4Ah)      - Adjust Block Size (SETBLOCK)
INT 21h (4Bh)      - Load or Execute (EXEC)
INT 21h (4Ch)      - Quit With Exit Code (EXIT)
INT 21h (4Dh)      - GET EXIT CODE OF SUBPROGRAM (WAIT)
INT 21h (4Eh)      - Find First ASCIIZ (FIND FIRST)
INT 21h (4Fh)      - Find Next ASCIIZ (FIND NEXT)
INT 21h (50h)      - Internal - Set PSP Segment
INT 21h (51h)      - Internal - Get PSP Segment
INT 21h (52h)      - Internal - Get Disk List
INT 21h (53h)      - Internal - Translate BPB
INT 21h (54h)      - Get Verify Flag
INT 21h (55h)      - Internal - Create PSP
INT 21h (56h)      - RENAME A FILE
INT 21h (57h)      - Get/Put Date/Time
INT 21h (58h)      - Get/Set allocation strategy (DOS 3.x)
INT 21h (59h)      - GET EXTENDED ERROR CODE (DOS 3.X)
INT 21h (5Ah)      - CREATE TMEPORARY FILE (DOS 3.x)
INT 21h (5Bh)      - CREATE NEW FILE (DOS 3.x)
INT 21h (5Ch)      - LOCK/UNLOCK FILE ACCESS (DOS 3.x)
INT 21h (5D06h)    - Internal - Get address of critical error flag
INT 21h (5Dh)      - Internal - Unknown
INT 21h (5E00h)    - Get Machine Name (DOS 3.1 + Microsoft Networks)
INT 21h (5E02h)    - Set Printer Setup (DOS 3.1 + Microsoft Networks)
INT 21h (5E03h)    - Get Printer Setup (DOS 3.1 + Microsoft Networks)
INT 21h (5F02h)    - Get Redirection List Entry (DOS 3.1 + Microsoft Networks)
INT 21h (5F03h)    - Redirect Device (DOS 3.1 + Microsoft Networks)
INT 21h (5F04h)    - Cancel Redirection (DOS 3.1 + Microsoft Networks)
INT 21h (60h)      - Internal - Resolve path string to fully qualified path string
INT 21h (61h)      - Internal - Unused (DOS 3.x)
INT 21h (62h)      - GET PSP ADDRESS (DOS 3.x)
INT 21h (63h)      - GET LEAD BYTE TABLE (DOS 2.25 only)
INT 21h (64h)      - Internal - unknown (DOS 3.3)
INT 21h (65h)      - GET EXTENDED COUNTRY INFORMATION (DOS 3.3)
INT 21h (66h)      - GET/SET GLOBAL CODE PAGE TABLE (DOS 3.3)
INT 21h (67h)      - SET HANDLE COUNT (DOS 3.3)
INT 21h (68h)      - COMMIT FILE - WRITE ALL BUFFERED DATA TO DISK (DOS 3.3)
INT 21h (E4h)      - DoubleDos -
INT 21h (EAh)      - DoubleDos - Turn off Task Switching
INT 21h (EBh)      - DoubleDos - Turn on Task Switching
INT 21h (ECh)      - DoubleDos - Get Virtual Screen Address
INT 21h (EEh)      - DoubleDos - Give away time to other tasks
INT 21h (FFh)      - CED installable commands