In the beginning of Ethernet, 10Base-5 used a very thick cable that was hard to work with (it was nicknamed thicknet). 10Base-2, which later replaced 10Base-5, used a much smaller cable, similar to that used for cable TV. Because the cable was much thinner than that used by 10Base-5, 10Base-2 was nicknamed thin-net. These cable technologies required large metal couplers called N connectors (10Base-5) and BNC connectors (10Base-2). These networks also required special terminators to be installed at the end of cable runs. When these couplers or terminators were removed, the entire network would stop working. These cables formed the physical backbones for Ethernet networks.
With the introduction of Ethernet running over unshielded twisted pair (UTP) cables terminated with RJ45 connectors, hubs became the new backbones in most installations. Many companies attached hubs to their existing thin-net networks to allow greater flexibility as well. Hubs were made to support UTP and BNC 10Base-2 installations, but UTP was so much easier to work with that it became the de facto standard.
A hub is simply a means of connecting Ethernet cables together so that their signals can be repeated to every other connected cable on the hub. Hubs may also be called repeaters for this reason, but it is important to understand that while a hub is a repeater, a repeater is not necessarily a hub.
A repeater repeats a signal. Repeaters are usually used to extend a connection to ...