Desktop systems continue to decrease in size and cost. They contain electronic and electromechanical components like motherboards, memories, input and output devices that allow them to run various operating systems. Clustering allows closely linked computer systems to share storage over a LAN, providing high-availability services. There are asymmetric and symmetric clustered systems that have features like node-to-node connectivity and support for LANs and WANs. Mobile computing devices like PDAs and smartphones can connect to networks and the internet but have limited size, memory and display compared to desktop systems.