Compatibility: 5.0+
Expects: AX    4b05H
DS:DX address of an ExecStateRec containing execution state info
Returns: none
Info: This function sets up DOS for executing a loaded program.
Specifically, it prepares DOS to correctly handle calls to Fn 30H
(get DOS version), as set up by the DOS Setver program.

DS:DX points to a block of memory prepared as an ExecStateRec that has
been filled with the information needed.

Notes:   This function is required by programs which intercept (and
replace) fn 4B00H (exec).

  After return, the caller should immediately begin executing the
program, specifically avoiding any DOS or BIOS fn calls.

  When DOS is installed in the HMA , this function turns off the
A20 line (making the HMA inaccessible).  DOS normally turns A20
on and leaves it on while executing other system functions.

See Also: Fn 4b00H (execute program)
Fn 4b01H (load program)
Fn 4b03H (load overlay)
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DOS Fn 4b05H: Set Execution State