Original PARC Smalltalk implementations had 32k (16b) word heaps (object pointers were 15b + one tag bit distinguishing SmallInteger and everything else). You could write quite complex systems with just that.

Edit: this is true for the canonical ST80 VM described in Blue book, ST80 VM on Alto AFAIK had some indirection mechanism (ie. not 32k words, but 32k heap objects) and did paging.