Yeah, the full 64k of RAM was never actually available. Only about 39K was directly available to the common user, but programmers could steal some extra memory from non-essential areas as I recall it.

What you could do is take advantage of disk memory to load more code / content, but then again, the disk was painfully slow for CBM's. Drives were very capable and 'intelligent' (having their own CPU's and RAM), but Commodore really fumbled the bag by not designing code to speed them up. You needed extra software or a cart to do that.