A packet switch is a switching node in a data transmission network which is using packets (as opposed to circuit-switching). They are connected to a number of physical network links in the overall network, and take packets in from one network interface, and send them out on another, as the packets moves from the source host to the destination.
The first packet switches were minicomputers provided with serial line interfaces (since synchronous serial lines the only data transmission technology available for the first packet data networks), such as the Interface Message Processors of the ARPANET.
The early generations of routers, used in the first decades of the Internet, were similar, but could use interfaces to the various local area network technologies (e.g. Ethernet). Only the very earliest used minicomputers; systems based on microprocessors were the usual for a long period thereafter.
More recently, very high speed packet switches use custom hardware.