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 Introduction
 Enhancements in DOS Versions 2 and 3
   Consistent Error Codes
   ASCIIZ Strings
   File Handles
   Installable Device Drivers
 Interrupt 21H Functions: DOS Versions 2.0 and Later
   Function 2FH (decimal 47): Get DTA Address
   Function 30H (decimal 48): Get DOS Version Number
   Function 31H (decimal 49): Terminate and Stay Resident
   Function 33H (decimal 51): Get/Set Ctrl-C Flag
   Function 35H (decimal 53): Get Interrupt Vector
   Function 36H (decimal 54): Get Disk Free Space
   Function 38H (decimal 56): Get/Set Country-Dependent Information
   Function 39H (decimal 57): Create Directory
   Function 3AH (decimal 58): Remove Directory
   Function 3BH (decimal 59): Change Current Directory
   Function 3CH (decimal 60): Create File
   Function 3DH (decimal 61): Open Handle
   Function 3EH (decimal 62): Close Handle
   Function 3FH (decimal 63): Read from File or Device
   Function 40H (decimal 64): Write to File or Device
   Function 41H (decimal 65): Delete File
   Function 42H (decimal 66): Move File Pointer
   Function 43H (decimal 67): Get/Set File Attributes
   Function 44H (decimal 68): IOCTL--I/O Control for Devices
   Function 45H (decimal 69): Duplicate Handle
   Function 46H (decimal 70): Force Duplicate Handle
   Function 47H (decimal 71): Get Current Directory
   Function 48H (decimal 72): Allocate Memory Block
   Function 49H (decimal 73): Free Memory Block
   Function 4AH (decimal 74): Resize Memory Block
   Function 4BH (decimal 75): EXEC--Load and Execute a Program
   Function 4CH (decimal 76): Terminate with Return Code
   Function 4DH (decimal 77): Get Return Code
   Function 4EH (decimal 78): Find First Matching Directory Entry
   Function 4FH (decimal 79): Find Next Matching Directory Entry
   Function 54H (decimal 84): Get Verify Flag
   Function 56H (decimal 86): Rename File
   Function 57H (decimal 87): Get/Set File Date and Time
   Function 58H (decimal 88): Get/Set Memory Allocation Strategy
   Function 59H (decimal 89): Get Extended Error Information
   Function 5AH (decimal 90): Create Temporary File
   Function 5BH (decimal 91): Create New File
   Function 5CH (decimal 92): Lock/Unlock File Region
   Function 5EH (decimal 94): Network Machine Name and Printer Setup
   Function 5FH (decimal 95): Network Redirection
   Function 62H (decimal 98): Get PSP Address
   Function 65H (decimal 101): Get Extended Country Information
   Function 66H (decimal 102): Get/Set Global Code Page
   Function 67H (decimal 103): Set Handle Count
   Function 68H (decimal 104): Commit File