mov     ax,1605h
        xor     dx,dx
        xor     cx,cx
        xor     dx,dx
        xor     si,si
        mov     ds,si
        mov     es,si
        mov     di,030Ah        ; windows version 3.10
        int     2Fh

        test    cx,cx           ; if cx=0 we can proceed
        jnz     some_error_handler
        mov     ax,ds
        or      ax,si
        jz      some_error_handler

; address of V86 toggle function is in ds:si. we store it for later use.
        push    ds si
        pop     [cs:v86switch]

        mov     ax,1608h        ; send startup complete
        int     2Fh

        xor     ax,ax           ; curcial part: we exit protected mode
        call    [cs:v86switch]  ; by calling function 0

        smsw    ax              ; check if protected mode is active
        test    ax,1            ; and if so, jump to an error handler
        jnz     some_error_handler

        call    set4gb          ; initialize flat real mode
        jc      some_error_handler

; here we have initialised flat real mode under emm386. we can do many
; things here, but when you return do _not_ forget to restore segment
; registers because EMM386 might not like to have 4 GB segments.
;
; restoring segment limits can be done by modifying the variables used to
; initialise flat real mode and then call flat real mode init again.

        mov     ax,1            ; switch to V86 mode with EMM function
        call    [cs:v86switch]

        mov     ax,1609h        ; begin exit
        int     2Fh
        mov     ax,1606h
        int     2Fh

some_error_handler:

        mov     ax,4C00h        ; here is it safe to exit to dos
        int     21h

set4gb: ;...
        ret

v86switch       dd ?
    

DOS is dead to some, yet others find it's a great programming environment for programs that run on other operating systems. Copy to floppy, run on machine 2, and you can still work in DOS while the blue screen of death wastes another half an hour on machine 2.

The DOS that came with Windoze 98 can be used as straight DOS programming in an old machine you would have thrown out anyway. Just set it up in directories and path like the old DOS was.

You can comment out EMM386 stuff in your autoexec.bat and config.sys with REM & reboot
REM emm386 (load some stuff here ####)
I hope this helps somehow. bitdog