DOS Fn 4b05H: Set Execution State

                                                         Compatibility: 5.0+ 
 Expects: AX    4b05H
          DS:DX address of an ExecStateRec containing execution state info
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 Returns: none
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    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
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