10BASE5 (also known as thick ethernet or thicknet) was the original commercially available variant of Ethernet. For its physical layer it used cable similar to RG-8/U coaxial cable but with extra braided shielding. This is a stiff, 0.375-inch (9.5 mm) diameter cable with an impedance of 50 ohms (?), a solid center conductor, a foam insulating filler, a shielding braid, and an outer jacket. The outer sheath was often yellow-to-orange/brown foam fluorinated ethylene propylene (for fire resistance) so it often is called "yellow cable", "orange hose", or sometimes humorously "frozen yellow garden hose".
10BASE5 has been superseded by much cheaper more convenient alternatives: first by 10BASE2 based on a thinner coaxial cable, and then once Ethernet over twisted pair was developed, by 10BASE-T and its successors 100BASE-TX and 1000BASE-T.
The name 10BASE5 is derived from several characteristics of the physical medium. The 10 refers to its transmission speed of 10 Mbit/s. The BASE is short for baseband signalling as opposed to broadband, and the 5 stands for the maximum segment length of 500 metres (1,600 ft).
10BASE5 coaxial cables had a maximum length of 500 meters (1,640 ft). The maximum number of nodes that can be connected to a 10BASE5 segment is 100. Transceivers may be installed only at precise 2.5-metre intervals. This distance was chosen to not correspond to the wavelength of the signal; this ensures that the reflections from multiple taps are not in phase. These suitable points are marked on the cable with black bands. The cable must be one linear run; T-connections are not allowed.
As is the case with most other high-speed buses, segments must be terminated with a resistor at each end. For coaxial-cable-based Ethernet, each end of the cable has a 50 ohm (?) resistor attached. Typically this resistor is built into a male N connector and attached to the end of the cable just past the last device. If termination is missing, or if there is a break in the cable, the AC signal on the bus is reflected, rather than dissipated when it reaches the end. This reflected signal is indistinguishable from a collision, and so no communication is possible.
Transceivers can be connected to cable segments with N connectors, or via a vampire tap, which allows new nodes to be added while existing connections are live. A vampire tap clamps onto the cable, forcing a spike to pierce through the outer shielding to contact the inner conductor while other spikes bite into the outer braided shield. Care must be taken to keep the outer shield from touching the spike; installation kits include a "coring tool" to drill through the outer layers and a "braid pick" to clear stray pieces of the outer shield.
Adding new stations to network was complicated by the need to accurately pierce the cable. The cable was stiff and difficult to bend around corners. One improper connection could take down the whole network and finding the source of the trouble was difficult.