Paging is a memory management technique used in computer operating systems to retrieve data from secondary storage and store it in main memory. In this technique, the physical memory is divided into fixed-size blocks called page frames, which are the same size as the pages used by the process. The operating system retrieves data from secondary storage in same-size blocks called pages. Paging is an important part of virtual memory implementations in modern operating systems, using secondary storage to let programs exceed the size of available physical memory.

Key features of paging include:

• Demand Paging: Pages are loaded only when they are referenced. A program from a memory-mapped file begins execution with none of its pages in RAM. As the program commits page faults, the operating system copies the needed pages from a file, e.g., memory-mapped file, paging file, or a swap partition containing the page data into RAM.
• Anticipatory Paging: Some systems use only demand paging—waiting until a page is actually requested before loading it into RAM.
• Protection and Sharing of Memory: Paging allows for the protection and sharing of memory between processes, as each process has its own page table that maps its logical address space to its physical address space.

Paging improves the efficiency of memory management by dividing memory into pages, and the operating system moves pages in and out of memory as needed. Keeping only the frequently used pages reduces the number of page faults, which improves system performance and responsiveness. Paging also allows for the allocation of memory on call for, which means that memory is most effectively allocated when it is needed.

In summary, paging is a memory management technique that allows for the efficient use of memory by dividing it into fixed-size blocks called pages, which are retrieved from secondary storage and stored in main memory as needed. It is an important part of virtual memory implementations in modern operating systems and allows programs to exceed the size of available physical memory.