DOS Fn 4b05H: Set Execution State

                                                         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)
          Process Control Functions
          Program Startup & Exit
          DOS Functions