Virtual Memory

operating-systems

Definition

Virtual Memory

Virtual memory is a memory management technique that provides a process with an “idealised” abstraction of storage resources, creating the illusion of a large, contiguous address space that is decoupled from the physical RAM.

Concepts

Decoupling

It separates the logical view of memory (contiguous, large) from the physical implementation (potentially fragmented, limited RAM). This allows the virtual address space to exceed the size of physical memory.

Resident Set

The resident set refers to the subset of a process’s pages that are currently residing in physical RAM.

Demand Paging

Pages of a process image are loaded from secondary storage (disk) to physical memory only when they are actually accessed. This is managed through page faults.

Advantages

• Concurrency: More processes can be maintained in memory simultaneously since only the active portions of each process need to be resident.
• Flexibility: Processes can be larger than the total physical memory available.
• Protection: Each process operates in its own isolated virtual address space.