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A ribbon cable, sometimes also called a multi-wire planar cable, is a type of electronic cabling that is characterized by its flat, flexible appearance. In many cases it resembles the sort of ribbon used in gift wrapping, which is where it gets its name. This sort of flexible cable was widely used in some of the earliest computer models, both as a means of internal wiring and as a way of connecting machines to other devices, particularly printers. The body of the cable or the “ribbon” itself is usually made up of much smaller insulated wires that are bound together to form a long, flat surface. Wires are often color-coded in terms of core function, and manufacturers usually also indicate direction by making the top or uppermost wire a distinctive color, typically red, in order for users to quickly be able to identify which way is up and which is down, for instance. In most cases the cables work through a series of conductors and connectors, and come in varying sizes depending on their main use. When they were first introduced, ribbon-style cables were widely considered to be industry standard. As technology has evolved, however, so has cabling technology, and these pieces have been largely replaced by smaller, rounded cables for both internal and external uses.
The ribbon style of cabling was first pioneered as a way to facilitate electromagnetic processing within early computer mainframes, but smaller versions can be found in a wide array of small electronics. The main idea with a ribbon-shaped cable is to harness a number of important wires together, and connect them as one — a concept that in many ways simplified electronics manufacturing as well as repair. Wires that are bundled are often easier to install and reattach.
Less frequently these cables were also used outside of machines, often as a way to connect one piece to another. They were some of the first to connect early computers to printers, for instance. While they aren’t normally used for power, nearly any messages that need to be communicated between devices can be carried over their wires very effectively.
In a ribbon cable, each wire — which is more formally known as a conductor — is used to connect two corresponding contacts. It is very important, then, that the correct wire attach to each end. Manufactures have introduced a color-coding system to simplify this process, and help prevent connecting the wrong contacts. The majority of the cables have a red band on one end, for instance, which helps users and technicians identify which end is the top or start. In another type, each wire is colored differently so that they can be easily identified; this variety is sometimes known as a "hippie cable."
Ribbon cables are distinguished by the number of conductors and the space between them. In most common size, the conductors are typically 0.05 inches (1.27 mm) apart; this allows for a connector with two rows, and a 0.1 inch (2.54 mm) pin spacing. This formation of ribbon is used most often for enclosed spaces. Cables can have as few as four connectors or as many as 80.
The cables' connecting ends are forced into a row of contacts in electronics through the ends of the cables. The connectors at the end of a ribbon cable are known as the insulation displacement connectors. On most of the cables there is an insulation displacement connector on both ends.
There are five basic connectors which are used in most electronics. The BT224 is the most common, and typically used in computers. PCB transition headers have the same set up as the BT224, but include a second row, while the BT224 has only one. D-subminiture connectors are found on printer ports; while most European computers and printers run off of the DIN41612 connector. DIL headers are commonly used for external connections.
It’s relatively rare to see ribbon-style cables on modern electronics, which is to say, electronics manufactured since about 2000. In smaller machines the flat surface is often thought to block airflow and create static, for instance, and they can be bulky and awkward to work with. In most places they’ve been replaced by sealed round cables that perform the same basic function, just with a more streamlined and compact shape.