HIMEM  |         
       | libs    
       |         
                 
HIMEM' |         
       | stack   
       |         
                 
       |         
       | free    
       |            
END    | rounded up to word

       |
       | variables, DIMs, strings
       |
LOMEM  | = TOP rounded up to word

TOP    |
       | program
       |
PAGE   | rounded up to word

END=x sets HIMEM and WimpSlot to x rounded up to
page size (8k per M of RAM)

HIMEM=x sets HIMEM to x rounded down to word.