Nowadays, thanks to advanced lithographic techniques, "wires" can be etched onto circuit boards at nanometer scales. The technology is to the point that these materials, as they grow ever smaller, cease to even be useful. Shrink your electronics down far enough and quantum mechanical effects take over and steal away the predictability required for computing utility. That is, we've reached a lower limit on the size of our wires, at least for now.
However, it wasn't all that long ago that circuits were wired on a very macro scale through the mostly forgotten process-slash-art known as wire wrapping. The idea is as you see it in the picture above: the bare, stripped end of a regular old insulated wire is wrapped around a pin or lead from an electrical component—a resistor or transistor or, really, any number of things—with the other end connecting to some other component. So, the delicate etching of a printed circuit board is replaced by bundles of colorful, clumsy wiring.
Wire wrapping had/has a crucial advantage over its alternatives. While the process actually lends itself very well to automation, the final product can still be manipulated and repaired by hand. The etchings of a PCB, not so much. In any case, wire wrapping, which is still sometimes used in prototyping, has an definite aesthetic.
Some examples—historical or otherwise—are below, with annotations where applicable:
The next three are back panels from different relatives of the PDP-10, a family of mainframe computers that were produced by DEC between 1966 and into the 1980s. A PDP-8 could be had for $18,000 and was capable of 312,500 addition operations per second.
The next several are more contemporary.
Motorola 6802-based prototype:
As circuitry chases after new and increasingly ingenious ways of making things still smaller, all but removing classical matter from computer engineering, wire wrapping seems like a tradition worth preserving. We can at least count on the small, intense army of breadboard tinkerers to provide some color. Similar idea, albeit without the actual wire wrapping.
Jumper cables will never go out of style.