Operating System Questions Long
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, and private address space, even if the physical memory is limited.
In a computer system, the memory is divided into fixed-size blocks called pages. Similarly, the secondary storage (usually a hard disk) is divided into fixed-size blocks called disk blocks or pages. The virtual memory system maps these pages of the process's address space to the physical memory or disk blocks.
When a program is executed, it is loaded into the physical memory in the form of pages. However, not all pages of a program are loaded into memory at once. Instead, the operating system uses a page table to keep track of which pages are currently in memory and which are on the disk.
When a program tries to access a page that is not currently in memory, a page fault occurs. The operating system then retrieves the required page from the disk and loads it into an available page frame in the physical memory. If there are no free page frames, the operating system selects a page to evict from memory, typically using a page replacement algorithm like the Least Recently Used (LRU) algorithm.
The page table is updated to reflect the new mapping of the page to the physical memory. The program's execution is then resumed, and it can access the requested page as if it were in memory all along. This process is transparent to the program, as it is unaware of the actual physical memory limitations.
Virtual memory provides several benefits. Firstly, it allows efficient utilization of physical memory by swapping pages in and out as needed. This enables running multiple programs simultaneously, even if the total memory required by all programs exceeds the available physical memory.
Secondly, virtual memory provides memory protection. Each process has its own virtual address space, ensuring that one process cannot access or modify the memory of another process. This enhances security and stability of the system.
Lastly, virtual memory simplifies memory management for programmers. They can write programs assuming they have a large address space, without worrying about the actual physical memory limitations. The operating system takes care of mapping the virtual addresses to physical memory or disk blocks.
In conclusion, virtual memory is a crucial component of modern operating systems. It allows efficient utilization of physical memory, provides memory protection, and simplifies memory management for programmers.