This article is from the Ethernet FAQ, by James Messer James@NetworkUptime.com with numerous contributions by others.
There are a number of physical networking components specified in
the IEEE 802.3 specification, but many of those early physical
networking components are not used in most modern Ethernet networks.
However, there may be instances where an existing legacy network
still exists which uses these older components. Since these older
pieces of equipment are still part of the 802.3 specification, there
are no technical reasons why an Ethernet network would not operate
properly with these components. The two most popular older Ethernet
technologies are 10BASE5 and 10BASE2.
10BASE5 is the original Ethernet backbone, and is occasionally
referred to as thicknet or thick Ethernet because of the thick 50
ohm coax that was used as the physical medium. 10BASE5 is a bus
topology that uses transceiver cables to attach stations to the
central 10BASE5 cable.
Maximum segment length: 500 meters
Maximum number of segments connected with repeaters: 5 (2500 meters)
Maximum attachments per segment: 100
Minimum separation between attachments: 2.5 meters
10BASE2 is designed as a smaller and less expensive alternative to
10BASE5, and is sometimes referred to as Thinnet or Thin Ethernet
because of the much smaller cables. 10BASE2 is also a bus topology,
but each of the workstations use a 'T' BNC connector to connect
workstations to the central bus.
Maximum segment length: 200 meters
Maximum number of segments connected with repeaters: 5 (1000 meters)
Maximum attachments per segment: 30
Minimum separation between attachments: .5 meters