This article is from the Token Ring FAQ, by James Messer James@NetworkUptime.com with numerous contributions by others.
Token ring connectivity requires three separate physical entities; a
Multistation Access Unit (MAU), a token ring lobe cable, and a token
ring adapter card.
A Multistation Access Unit (MAU or MSAU) is a hub-like device that
connects to all token ring stations. Although the token ring
stations are attached to the MAU in a physical star configuration, a
true ring is maintained inside the MAU.
Unlike an Ethernet hub, a MAU consists of physical or electronic
relays which keep each station in a loopback state until a voltage
is sent from the station to the MAU. Since this voltage does not
affect data communications, it is referred to as a 'phantom'
voltage. Once this phantom voltage is received by the MAU, a relay
is activated that inserts the token ring station onto the ring.
MAUs are connected together with Ring In/Ring Out (RI/RO) cables. To
maintain a true ring, both the RI and the RO ports must be connected
from one MAU to the other.
A token ring lobe cable connects the token ring station to the MAU.
This cable communicates over four wires; two for transmit and two
for receive. The cable can be Shielded Twisted Pair (STP) or
Unshielded Twisted Pair (UTP).
A token ring adapter card is the physical interface that a station
uses to connect to a token ring network. There are token ring
adapter cards for almost every computer bus type.