In telecommunications wire wrap is in common high volume use in modern communications networks for cross connects of copper wiring. Electronic components mounted on an insulating board are interconnected by lengths of insulated wire run between their terminals, with the connections made by wrapping several turns of uninsulated sections of the wire around a component lead or a socket pin. Another optimization is that within each length and color of wire, the computer selects the next wire so that the wrap head moves to the nearest pin that is to the right of the previous pin. Wire wrapping was used for splices and for finishing cable ends in suspension bridge wires and other wire rope rigging, usually with a smaller diameter wire wrapped around a larger wire or bundle of wires. The most common insulation is "Kynar". The larger posts can be rewrapped hundreds of times. Above the turn of insulated wire, the bare wire wraps around the post. The result is that 1.5 to 2 turns of insulated wire are wrapped around the post, and above that, 7 to 9 turns of bare wire are wrapped around the post. The automatic wire wrap machines themselves were quite large, 6 ft (1.8 m) tall and 8 ft (2.4 m) square. Fully automated wire-wrap machines don't care. Servicing the machines was extremely complex, and often meant climbing inside them just to work on them. Wire-wrap works well with digital circuits with few discrete components, but is less convenient for analog systems with many discrete resistors, capacitors or other components (such elements can be soldered to a header and plugged into a wire wrap socket). The machines were driven by wiring instructions encoded onto punched cards, Mylar punched hole tape, and early micro computers. This permits manual wire-wrapping to be used for repairs. Usually blue is used for bottom wires, and yellow for top wires. The tool was marketed under its original name – since the name of the manufacturer was coincidentally the same as the name of the inventor. A template is map of a device's pins. It is unique among automated prototyping techniques in that wire lengths can be exactly controlled, and twisted pairs or magnetically shielded twisted quads can be routed together. This is easy: Start with the bottom. The post has room for three such connections, although usually only one or two are needed. This reduces vibration of the longer wires, making the board more rugged in a vibrating environment such as a vehicle. Also, to make the layers easier to see, they are made with different colors of insulation. [1][2] The square hard-gold-plated post thus forms 28 redundant contacts. At the same time, it recalculates the wire's length so that it can be correctly routed. The sockets have square posts. Epoxy is never used for the coating because it makes an assembly unrepairable. The next step was to encode the pin positions of every device. If wires must be routed in lanes (required for some high-frequency or low-noise signals), a separate routing program reads a "lane" file to find where the lane-routed wires can be placed on a board. In wire-wrapping, electronic design automation can design the board, and optimize the order in which wires are placed. Long wires are usually placed first within a level so that shorter wires will hold longer wires down. Solder-less breadboards and the decreasing cost of professionally made PCBs have nearly eliminated this technology. In the middle 1980s they were gradually replaced by connectorized cables. The guns are manually pulled down, and the trigger pressed to make a wrap. IBM's first transistorized computers, introduced within the late 1950s, were built with the IBM Standard Modular System that used wire-wrapped backplanes. Manual annotation is usually still required for special signals, such as high-speed, high current or noise-sensitive circuits, or special construction techniques such as twisted pairs or special routing. [3] The sockets are an additional cost compared to directly inserting integrated circuits into a printed circuit board, and add size and mass to a system. Surface-mount technology has made the technique much less useful than in previous decades. The wire list is then sorted alphabetically into an optimal assembly sequence. Such tools were used in large numbers in American telephone exchanges in the last third of the 20th century, usually with a bigger bit to handle 22 or 24 AWG wire rather than the smaller 28 or 30 AWG used in circuit boards and backplanes.