Hot swapping is the replacement or addition of components to a computer system without stopping, shutting down, or rebooting the system; hot plugging describes the addition of components only. Components which have such functionality are said to be hot-swappable or hot-pluggable; likewise, components which do not are cold-swappable or cold-pluggable.
Hot-swapping a hard drive in a storage server
Sun SPARCstation hot swappable Single Connector Attachment (SCA) drive cradle[citation needed]
A server is a computer that provides information to other computers called "clients" on computer network. This architecture is called the client–server model. Servers can provide various functionalities, often called "services", such as sharing data or resources among multiple clients or performing computations for a client. A single server can serve multiple clients, and a single client can use multiple servers. A client process may run on the same device or may connect over a network to a server on a different device. Typical servers are database servers, file servers, mail servers, print servers, web servers, game servers, and application servers.
Wikimedia Foundation rackmount servers on racks in a data center
The first WWW server is located at CERN with its original sticker that says: "This machine is a server. DO NOT POWER IT DOWN!!"
A rack-mountable server with the top cover removed to reveal internal components
A server rack seen from the rear