under the v-system, objects in servers were referred to via an "ad hoc" private key of some sort, say a 32-bit integer. clients would pass these keys into the servers in order to maintain a conversation about a specific task. for instance, an application might ask the kernel for the "file system" and be handed a 32-bit key representing a program id, and then use that key to send a message to the file system asking it to open the file "my addresses", which would result in a 64-bit key being handed back. the keys in this example are proprietary to the servers, there was no common key format being used across the system.