For reading from and writing to structures within cells, Cosmos uses a local addressing scheme for each structure (i.e. the first bit of the Genome, of the Communications Working Memory, and of the messages in the Received Message Store, are all treated as address zero within that particular structure). Cells have no knowledge of their memory location (or that of other cells) in the global addressing scheme of the system. This is in contrast to Tierra, which uses a global addressing scheme. The only ways that cells can interact with each other are therefore by communication; by physical contact, such as by extracting energy tokens from each other (which is possible when the parameter energy_collection_scheme is set to shared--see Section 4.5.3) and slowing down passing organisms (see Section 4.5.4); and, for cells within a multicellular organism, by the exchange of regulators and energy tokens.