The Super Node is an object implemented in user code that is externally like a node but with a limit of 232 slots. It is implemented as a variable hight tree of nodes.
The super node is the main tool of the key cache which some programs use when they must hold many keys. The two programs to which this was critical are the binder and the debugger. It was the default facility for PL/I programs. The performance of the key cache was disappointing. It was a factor of several performance penalty.