Your gunna have to give us some more information, what are you trying to save, where specifically are you trying to save it? Does it matter where its saved, ie non vol? Give us something to work with lol.
You don't mention which memory would that be. Because strictly translating the question, there is now difference between 89c2051 MCU and any other if it is about RAM. It is C we are talking about right? You just declare a variable (which obviously occupies memory space) and write values on that variable. Maybe you need absolute addressing? It would then help if you mentioned your compiler, so other members using the same compiler can help you.