OSDev.org

every example ive seen uses code like this to enable a20 line:

    call keyboard_wait
    mov al,0D1h
    out 64h,al
    call keyboard_wait
    mov al,0DFh
    out 60h,al

but when i poke the 3 megabyte mark
the value gets written to 2 megabyte.
that means the a20 line is still closed right?

so i tried using the code thats supposed to close the a20 line:

    call keyboard_wait
    mov al,0D1h
    out 64h,al
    call keyboard_wait
    mov al,0DDh
    out 60h,al

and now it doesnt write to 2 megabyte
what does it mean?
are all the examples wrong?
and how can i make sure the a20 line is open?