Important Notice

The pages on this site contain documentation for very old MS-DOS software, purely for historical purposes. If you're looking for up-to-date documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.

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  MS-DOS then takes the following actions:
 
▀ Flushes the file buffers and closes any open handles for files or devices
  owned by the process.
 
▀ Restores the termination handler vector (Int 22H) from PSP:000AH.
 
▀ Restores the CTRL+C handler vector (Int 23H) from PSP:000EH.
 
▀ Restores the critical-error handler vector (Int 24H) from PSP:0012H.
 
▀ Transfers control to the termination handler.
 
▀ If the program is returning to COMMAND.COM, control transfers to the
  resident portion, and the transient portion is reloaded if necessary. If
  a batch file is in progress, the next line of the file is fetched and
  interpreted; otherwise, a prompt is issued for the next user command.
 
▀ This function call is typically used to allow user-written utilities,
  drivers, or interrupt handlers to be loaded as ordinary .COM or .EXE
  programs and then remain resident. Subsequent entrance to the code is via
  a hardware or software interrupt.
 
▀ This function attempts to set the initial memory allocation block to the
  length in paragraphs specified in register DX. If other memory blocks
  have been requested by the application using Int 21H Function 48H, they
  will not be released by this function.
 
▀ Other methods of performing a final exit are:
  - Int 20H
  - Int 21H Function 00H
  - Int 21H Function 4CH
  - Int 27H
 
▀ The return code may be retrieved by a parent process through Int 21H
  Function 4DH (Get Return Code). It can also be tested in a batch file
  with an IF ERRORLEVEL statement. By convention, a return code of zero
  indicates successful execution, and a non-zero return code indicates an
  error.
 
▀ This function should not be called by .EXE programs that are loaded at
  the high end of the transient program area (i.e., linked with the /HIGH
  switch) because doing so reserves the memory that is normally used by the
  transient part of COMMAND.COM. If COMMAND.COM cannot be reloaded, the
  system will fail.
 
▀ This function should be used in preference to Int 27H because it supports
  return codes, allows larger amounts of memory to be reserved, and does
  not require CS to contain the segment of the program segment prefix.
 
▀ [3.0+] If the program is running on a network, it should remove all locks
  it has placed on file regions before terminating.
                                    -♦-