Auxiliary memory (also referred to as secondary storage) is the non-volatile memory lowest-cost, highest-capacity, and slowest-access storage in a computer system. It is where programs and data kept for long-term storage or when not in immediate use.
Such memories tend to occur in two types-sequential access (data must access in a linear sequence) and direct access (data may access in any sequence). The most common sequential storage device is the hard disk drives, whereas direct-access devices include rotating drums, disks, CD-ROMs, and DVD-ROMs.It used as permanent storage of data in mainframes and supercomputers.
Auxiliary memory may also refer to as auxiliary storage, secondary storage, secondary memory, external storage or external memory. Auxiliary memory is not directly accessible by the CPU; instead, it stores noncritical system data like large data files, documents, programs and other back up information that supplied to primary memory from auxiliary memory over a high-bandwidth channel, which will use whenever necessary. Auxiliary memory holds data for future use, and that retains information even the power fails.