INT 21 - DOS 5.0 - SET EXECUTION STATE
AX = 4B05h
DS:DX -> execution state structure (see below)
Return: CF clear if successful
AX = 0000h
CF set on error
AX = error code (see AH=59h)
Note:   used by programs which intercept AX=4B00h to prepare new programs for
execution (including setting the DOS version number).  No DOS, BIOS
or other software interrupt may be called after return from this call
before commencement of the child process.  If DOS is running in the
HMA, A20 is turned off on return from this call.

Format of execution state structure:
Offset  Size    Description
00h    WORD    reserved (00h)
02h    WORD    type flags
bit 0: program is an .EXE
1: program is an overlay
04h    DWORD   pointer to ASCIZ name of program file
08h    WORD    PSP segment of new program
0Ah    DWORD   starting CS:IP of new program
0Eh    DWORD   program size including PSP

See also: 214B

214B05 - DOS 5.0 - SET EXECUTION STATE