It is one of IBM's crown jewels and can display all volumes – memory, solid-state, and turntable – as a single address space. The OS only sees an extensive set of default addresses (64-bit eligible since 1991 and 48-bit eligible since 1978!). This means system administrators and application developers don't have to worry about existing storage systems.What is Single-Level Storage?
Single-level Storage specifies "two-dimensional" levels of "unlimited" computer storage to addresses, pages, or objects. Pages can be in primary storage (RAM) or secondary Storage (disk). The current location of the address is not essential for processing. IBM iSeries is responsible for finding and processing pages on a computer system rather than a system engineer or programmer. If the page is in primary storage, it will be available immediately. IBMi brings the page to the primary volume if the page is on disk. I/O processes do no explicit secondary storage.