This article is from the Token Ring FAQ, by James Messer James@NetworkUptime.com with numerous contributions by others.
Token ring runs at speeds of 4 megabits per second (500,000 bytes
per second) and 16 megabits per second (2,000,000 bytes per second).
Some token ring switches support a non-standard referred to as
Direct Token Ring (DTR), or full-duplex token ring. This allows for
16 megabit speeds in the sending and receiving directions
simultaneously, for a maximum of 32 megabits per second (4,000,000
bytes per second).