Clients, Servers and Hosts

Kite Studio keeps its project files on a small box in the rack called files. When Asha's laptop pulls a design from it, which one is the server? Easy. But when two designers share a file directly between their laptops, the easy answer stops working. The words client, server and host describe roles, not shapes of hardware.

The rule

Every device on the network is a host; its role decides client or server.

Host. Any device with a network address that can send and receive traffic: laptops, phones, the printer, the files box, even a smart TV. If it has an IP address on the network, it is a host.

Client. The side that starts the conversation and asks for something: "send me this web page", "give me that file". Asha's browser is a client.

Server. The side that waits for requests and answers them. A server program listens on the network all day. The files box runs a file-sharing service, so it acts as a server. "Server" often also names the powerful machine that runs such programs, but the role is what matters: an ordinary laptop running a web service is a server for that service.

Two ways to organise hosts.

• Client-server network: a few central servers hold the data and the many clients ask them. Kite Studio's shared folder works this way. It is easy to back up, secure and manage in one place, but if files goes down, nobody can reach their projects.
• Peer-to-peer (P2P) network: every host, called a peer, can both ask and answer. Two laptops swapping files directly form a tiny P2P network. There is no central point to fail, but also no central place to control access or keep backups.

The shortcut

Point at a conversation, not a box, and ask: "Who spoke first?" Whoever started the exchange is the client for that exchange; whoever was listening is the server. Then ask: "Can the listener also start conversations of its own?" If every host does both, it is peer-to-peer.

The trap is thinking "server" means "big machine in a rack". A single device can be a server for one conversation and a client for the next.

Drills

Answer fast — trust the rule.

Remember

• Every device with a network address is a host; its role in a conversation decides client or server.
• Ask "who spoke first?" — the starter is the client, the listener is the server.
• Client-server is easy to manage but has a central point of failure; peer-to-peer has none, but also no central control.