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  Interrupt:   21h     Function:   3Fh
 
  Title:       Read File or Device
 
  See also:    Write to File or Device, Set File Pointer, @Read
 
  Description:
 
     Given a valid file handle from a previous open or create
     operation, a buffer address, and a length in bytes, this function
     transfers data at the current file pointer position from the file
     into the buffer and then updates the file pointer position.
 
     Input                                Output
 
     AH = 3Fh                             If function successful
     BX = Handle                            Carry flag: clear
     CX = Number of bytes to read           AX = Bytes transferred
     DS:DX = segment:offset of buffer
                                          If function unsuccessful
                                            Carry flag: set
                                            AX = Error code (05h or 06h)
                                            See: ◄Error codes►
                                    -♦-