A network is two or more devices connected so they can share data and resources.

• LAN (local area network): a small area such as one building; the organisation owns the hardware.
• WAN (wide area network): a large area, linking LANs over lines rented from other companies. The internet is the biggest WAN.

Client-server: a central server stores files, accounts and services; clients request them. Easy to back up and secure centrally, but servers cost money and need managing, and a server failure affects everyone.

Peer-to-peer: every computer is both client and server. Cheap and simple for a few machines, but there is no central backup or security.

Hardware	Job
NIC (network interface controller)	lets a device connect to a network; has the MAC address
Switch	connects devices on a LAN and sends each frame only to the device it is for
Router	forwards packets between networks, such as a LAN and the internet
Wireless access point	lets devices join the network by Wi-Fi

Transmission media: copper cable (cheap, short distances), fibre optic (light, very fast over long distances), radio waves (Wi-Fi: no cables, but slower, shorter range, more interference, and must be encrypted).

Performance depends on bandwidth, the number of users sharing it, the media, distance, interference and latency.