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 Introduction
 Interrupt 21H Functions: DOS Version 1
   Function 00H (decimal 0): Terminate
   Function 01H (decimal 1): Character Input with Echo
   Function 02H (decimal 2): Character Output
   Function 03H (decimal 3): Auxiliary Input
   Function 04H (decimal 4): Auxiliary Output
   Function 05H (decimal 5): Printer Output
   Function 06H (decimal 6): Direct Console Input/Output
   Function 07H (decimal 7): Direct Console Input Without Echo
   Function 08H (decimal 8): Console Input Without Echo
   Function 09H (decimal 9): String Output
   Function 0AH (decimal 10): Buffered Keyboard Input
   Function 0BH (decimal 11): Check Keyboard Status
   Function 0CH (decimal 12): Flush Keyboard Buffer, Read Keyboard
   Function 0DH (decimal 13): Flush Disk Buffers
   Function 0EH (decimal 14): Select Disk Drive
   Function 0FH (decimal 15): Open File
   Function 10H (decimal 16): Close File
   Function 11H (decimal 17): Find First Matching Directory Entry
   Function 12H (decimal 18): Find Next Matching Directory Entry
   Function 13H (decimal 19): Delete File
   Function 14H (decimal 20): Sequential Read
   Function 15H (decimal 21): Sequential Write
   Function 16H (decimal 22): Create File
   Function 17H (decimal 23): Rename File
   Function 19H (decimal 25): Get Current Disk
   Function 1AH (decimal 26): Set Disk Transfer Area
   Function 1BH (decimal 27): Get Default Drive Information
   Function 1CH (decimal 28): Get Specified Drive Information
   Function 21H (decimal 33): Read Random Record
   Function 22H (decimal 34): Write Random Record
   Function 23H (decimal 35): Get File Size
   Function 24H (decimal 36): Set FCB Random Record Field
   Function 25H (decimal 37): Set Interrupt Vector
   Function 26H (decimal 38): Create New Program Segment Prefix
   Function 27H (decimal 39): Read Random Records
   Function 28H (decimal 40): Write Random Records
   Function 29H (decimal 41): Parse Filename
   Function 2AH (decimal 42): Get Date
   Function 2BH (decimal 43): Set Date
   Function 2CH (decimal 44): Get Time
   Function 2DH (decimal 45): Set Time
   Function 2EH (decimal 46): Set Verify Flag
 The File Control Block
   FCB Fields
   Extended FCB Fields
 An Example