A media attachment unit (MAU) is a device that attaches computers to an Ethernet backbone. The device uses the attachment unit interface port on a computer to connect one or more stations to an Ethernet network that do not have Ethernet network cards installed in them.
The common terminology seen when referring to a MAU is a token ring. The computers on the token ring are daisy chained together and each section of the network is connected to a MAU. The MAU is then connected to the Ethernet LAN.
The media attachment unit is used to exchange data or tokens between computers connected to it and other computers connected to the LAN via Ethernet. The token portion of a token ring network describes the method used to detect collisions between data transmissions and retries the submissions to ensure that data is delivered.
A media attachment unit can be built into computers or can be a separate device which many computers are connected to. The best way to understand how a network using a media attachment unit operates is to think of the device as separate from the PC. A group of several PCs will likely be connected to the same MAU. As one computer sends packets to the network, other computers may also be transmitting. It is the function of the MAU to ensure that each PC is able to transmit data, by providing a token to each PC for a predetermined amount of time. During this time, the PC holding the token can transmit data. This helps reduce the number of collisions between data packets traversing the network.
In recent years, the token ring implementation has fallen out of favor to Ethernet network interface cards which are typically built in to newer computers and operate at much faster speeds than a token ring network using media attachment units can operate. A token ring network can operate at 4 or 16 megabits per second, where an Ethernet based network and computers connected directly with network interface cards can operate at speeds of 10, 100, or even 1000 megabits per second.
As computers became faster and networks more prevalent, the media attachment unit and token ring network became much too slow to handle the applications and bandwidth supplied and used by the newer equipment. There are some fiber based networks that work similarly to a token ring network, but the cost to implement these technologies is very high and not practical for many organizations.