40fe0930_Reviewing_Where_We_Stand__EROS
[0] 5. [UNIX] Metadata is Hidden. The process control block is a primary kernel concept, and the address mapping data structure and file metadata structure representations are private to the operating system. This permits the kernel to leverage some amount of higher-level semantic knowledge in the interests of performance. [EROS] 
Metadata is Exposed. The composition of address spaces and processes from nodes is explicit. This is driven by persistence and is usually value-neutral, but introduces the possibility that objects may come to be composed from mixed storage sources, which is a semantic disaster.
Reviewing Where We Stand
EROS