A server is a computer that is linked to a network of other workstations known as "clients." Client computers use the network to request information from the server. Servers often offer greater storage, memory, and computing power than standard workstations. They are usually dedicated to only one task - storing data for other computers and serving pages when requested by clients. The most common type of server is the web server. It provides access to files that contain information used by websites to create pages that can be viewed by visitors. Web servers communicate with browsers which display downloaded pages. Some servers, such as mail servers, provide services for applications which require constant communication with many users, such as email clients or news readers. Other servers, such as DNS (domain name service) servers, allow computers to connect to other computers or devices using text-based protocols such as HTTP (hypertext transfer protocol). Servers have various features that enable them to better serve their clients. For example, some servers are "virtual," meaning they appear to be several different computers connected to each other. This is useful because it allows server administrators to add and remove computers without disrupting the operation of the server. Virtual servers also allow server resources to be shared across many users, reducing the amount of hardware needed. Virtual servers are commonly used by Internet businesses that want to make sure that clients do not experience performance issues while still needing to scale up quickly if their traffic increases.