What device is Emily using if every computer on her home network received the file she sent?

Emily is using a hub if every computer on her home network received the file she sent. A hub operates at the physical layer of the OSI model and is designed to broadcast data packets to all devices connected to it in the network. This means that when a file is sent from one computer, the hub sends a copy of this file to every other device on the network. As a result, all computers on the local network receive the same data simultaneously.

In contrast, a router directs data traffic between different networks and typically sends information only to the specific device intended to receive it, rather than broadcasting it to all devices. A switch, while also connecting devices within a network, operates more intelligently than a hub; it learns the MAC addresses of the devices on the network and sends data only to the intended recipient rather than broadcasting it. A firewall, on the other hand, is primarily used for security purposes and regulates traffic entering or leaving a network based on predefined security rules, rather than facilitating data sharing among devices.

Therefore, given the nature of data transmission described, a hub is the correct device used by Emily for sending the file to all computers on her home network.