Internal EPROM is addressed,
a) if EA# = VCC
- low program memory (e.g. 4 kByte) is internal
- high program memory (above internal) is external

b) if EA# = GND
- program memory is external

External RAM is addressed using MOVX instructions

You'll find all information in http://www.atmel.com/atmel/acrobat/doc0497.pdf