Explain the concept of virtual memory.

Virtual memory is a memory management technique used by operating systems to provide an illusion of having more physical memory than is actually available. It allows programs to execute as if they have access to a large, contiguous block of memory, even if the physical memory is limited.

In virtual memory, the memory address space of a process is divided into fixed-size blocks called pages. Similarly, the physical memory is divided into blocks called frames. The operating system maintains a mapping table called the page table, which keeps track of the correspondence between the virtual pages and the physical frames.

When a program references a memory address, the processor first checks the page table to determine if the corresponding page is in physical memory. If it is, the processor directly accesses the physical memory. However, if the page is not present in physical memory, a page fault occurs.

During a page fault, the operating system selects a page to evict from physical memory and replaces it with the requested page from the disk. This process is known as page swapping or paging. The evicted page is written back to the disk if it has been modified.

Virtual memory provides several benefits. It allows for efficient memory utilization by allowing multiple processes to share the same physical memory. It also enables the execution of programs that require more memory than is physically available, as the operating system can swap pages in and out of disk storage as needed.

Furthermore, virtual memory provides memory protection by assigning each process its own virtual address space. This prevents one process from accessing or modifying the memory of another process. It also simplifies memory management for programmers, as they can write programs assuming they have access to a large amount of memory, without worrying about the physical limitations.

In summary, virtual memory is a memory management technique that allows programs to access more memory than is physically available. It provides efficient memory utilization, enables the execution of memory-intensive programs, and offers memory protection and simplicity for programmers.