What lead to the concept of paging?

The main memory is separated into two parts that are one for the resident operating system, and one for the user processes. We may perhaps place the OS in either low memory or high memory. But typically we want several user processes to reside in memory at the same time. In the contiguous memory allocation every process is contained in a single contiguous section of memory. However it's not possible to allocate contiguous memory for all the processes waiting in the input queue. Here comes the requirement for a new memory management technique.

Two other important factors that lead to the development of paging are internal and external fragmentation.