Figure 2-1
A node is 16 slots and a single boolean value called the process-running bit. A slot is a storage area for one key. A node is completely described by giving the contents of its 16 slots and the process-running bit. Nodes are not directly accessible to System/370 problem mode instructions. Nodes and their contents may be accessed by invoking keys.
A node that has the process-running bit TRUE will be viewed as a domain root by the kernel. Processes have no identity in themselves, so it is not meaningful to ask which process is associated with a given node. Start and resume keys can be used, by invoking them, to change the state of the process-running bit. There is no explicit test for the process-running bit.
Design note: It is necessary to hide the process-running bit to ensure that meters can stop domains non-destructively.