Memory Organization

IOS maps the entire physical memory into one large flat virtual address space. The CPU's MMU is used when available to create the virtual address space even though IOS doesn't employ a full virtual memory scheme. To reduce overhead, the kernel does not perform any memory paging or swapping, so virtual address space is limited to the bounds of the physical memory available.

IOS divides this address space into areas of memory called regions,which mostly correspond to the various types of physical memory. For example, SRAM might be present for storing packets and DRAM might be present for storing software and data on a given type of router. Classifying memory into regions allows IOS to group various types of memory so software needn't know about the specifics of memory on every platform.