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▀ The parameter block format for Subfunction 00H (Load and Execute Pro-
  gram) is as follows:
 
  Bytes    Contents
  ═══════  ═══════════════════════════════════════════════════
  00H-01H  Segment pointer to environment block
  02H-03H  Offset of command line tail
  04H-05H  Segment of command line tail
  06H-07H  Offset of first FCB to be copied into new PSP+5CH
  08H-09H  Segment of first FCB
  0AH-0BH  Offset of second FCB to be copied into new PSP+6CH
  0CH-0DH  Segment of second FCB
 
▀ The parameter block format for Subfunction 03H (Load Overlay) is as
  follows:
 
  Bytes    Contents
  ═══════  ═════════════════════════════════════════════
  00H-01H  Segment address where overlay is to be loaded
  02H-03H  Relocation factor to apply to loaded image
 
▀ The environment block must be paragraph aligned. It consists of a se-
  quence of ASCIIZ strings in the form:
 
  db     'COMSPEC=A:COMMAND.COM',0
 
  The entire set of strings is terminated by an extra null (00H) byte.
 
▀ The command tail format consists of a count byte, followed by an ASCII
  string, terminated by a carriage return (which is not included in the
  count). The first character in the string should be an ASCII space (20H)
  for compatibility with the command tail passed to programs by
  COMMAND.COM. For example:
 
  db     6,' *.DAT',0dh
 
▀ Before a program uses Int 21H Function 4BH to run another program, it must
  release all memory it is not actually using with a call to Int 21H Func-
  tion 4AH, passing the segment address of its own PSP and the number of
  paragraphs to retain.
 
▀ Ordinarily, all active handles of the parent program are inherited by
  the child program, although the parent can prevent this in MS-DOS 3.0
  and later by setting the inheritance bit when the file or device is
  opened. Any redirection of the standard input and/or output in the
  parent process also affects the child process.
 
▀ The environment block can be used to pass information to the child pro-
  cess. If the environment block pointer in the parameter block is zero,
  the child program inherits an exact copy of the parent's environment.
  In any case, the segment address of the child's environment is found at
  offset 002CH in the child's PSP.
 
▀ After return from the EXEC function call, the termination type and
  return code of the child program may be obtained with Int 21H Function
  4DH.
                                    -♦-