input: [0] 3. [UNIX] There are two memory models: persistent and ephemeral. Main memory is ephemeral, and programs must make special provisions to get their state preserved across system shutdown. Consistency must be managed explicitly, even within a single node. [EROS] 
output: There is an implicitly persistent, unified memory model. Main memory has the same semantics as disk storage, and survives system shutdown/restart. As part of this, there is a global (machine-wide) consistency model that allows objects to share a common understanding of their mutual states without heavyweight transactions.