IBM's key innovation in operating systems in this class (which they call "mid-range"), was their "CPF" for the System/38. This had capability-based addressing, used a machine interface architecture to isolate the application software and most of the operating system from hardware dependencies (including even such details as address size and register size) and included an integrated RDBMS. The succeeding OS/400 for the AS/400 has no files, only objects of different types and these objects persist in very large, flat virtual memory, called a single-level store. i5/OS and later IBM i for the iSeries continue this line of operating system.