About ascess Ram's certain address

Dear sir,

i just got a testing board,which contain a P89c51rd2.
The port 0 and port 2 (lower 4 bit) is connect to a external ram DS1643(8k).

As the DS1643 contain a real time clock inside it at the final eight byte.

I want to ask that
1. how can i know the starting and ending
address of the external ram.

2. Moreover, when a external rom is also
connected to it, how can i know the
rom's address?

3. Is it possible for me to allocate
address to it?

would you my give some advice to me, and any referance material from the web?

thx!

Raul