Function 4B01h          Load Program

    Loads a program into memory and creates a new program segment
    prefix (PSP), but does not transfer control to the new program.

        Entry   AX    = 4B01h
                DS:DX = Pointer to ASCIIZ program name (.COM or .EXE)
                ES:BX = Pointer to a Load structure

        Return  Expect all registers to be changed, except CS:IP
                AX = Error code, if CF is set
                     | 01h Invalid function number
                     | 02h File not found
                     | 03h Path not found
                     | 04h No handle available
                     | 05h Access denied
                     | 08h Insufficient memory
                     | 0Ah Invalid environment
                     | 0Bh Invalid format

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    Before function 4B01h is invoked, DS:DX must point to a zero-
    terminated string that specifies the program to load. The program
    name must be a valid DOS filename, and the file must be a valid
    .COM or .EXE program. ES:BX must point to a Load structure.

    There must be enough free memory for DOS to load the program file.


    Function 4b01h was undocumented prior to the release of DOS 5.0.