Blinkenlights

In computer jargon, blinkenlights are diagnostic lights on front panels of old mainframe computers. More recently the term applies to status lights of modern network hardware (modems, network hubs, etc.). Blinkenlights disappeared from more recent computers for a number of reasons, the most important being the fact that with faster CPUs a human can no longer interpret the processes in the computer on the fly. Though more sophisticated UI mechanisms have since been developed, blinkenlights may still be present as additional status indicators and familiar skeuomorphs.

Etymology
The term has its origins in hacker humor and is taken from a famous (often blackletter-Gothic) mock warning sign written in a mangled form of German. Variants of the sign were relatively common in computer rooms in English-speaking countries from the early 1960s. One version read:

Some versions of the sign end with the word blinkenlights.

The sign dates back as far as 1955 at IBM, and a copy was reported at London University's Atlas computer facility.

Although the sign might initially appear to be in German and uses an approximation of German grammar, it is composed largely of words that are either near-homonyms of English words or (in the cases of the longer words) actual English words that are rendered in a faux-German spelling. As such, the sign is generally comprehensible by many English speakers regardless of whether they have any fluency in German, but mostly incomprehensible to German speakers with no knowledge of English. Much of the humor in these signs was their intentionally incorrect language.

Michael J. Preston relates the sign as being posted above photocopiers in offices as a warning not to mess with the machine in the first print reference from 1974. The sign is also reported to have been seen on an electron microscope at the Cavendish Laboratory in the 1950s. Such pseudo-German parodies were common in Allied machine shops during and following World War II, and an example photocopy is shown in the Jargon File.

The Jargon File also mentions that German hackers had in turn developed their own versions of the blinkenlights poster, in broken English:

Actual blinkenlights


The bits and digits in the earliest mechanical and vacuum tube-based computers were typically large and few, making it easy to see (and often hear) activity. Afterwards, for decades, computers incorporated arrays of indicator lamps in their control panels, indicating the values carried on the address, data, and other internal buses, and in various registers. These could be used for diagnosing or "single-stepping" a halted machine, but even with the machine operating normally, a skilled operator could interpret the high-speed blur of the lamps to tell which section of a large program was executing, whether the program was caught in an endless loop, and so on.

With rising processor clock rates, increased memory sizes, and improved interactive debugging tools, such panel lights gradually lost their usefulness, though today most devices have indicators showing power on/off status, hard disk activity, network activity, and other indicators of "signs of life".

The Connection Machine, a $65,536$-processor parallel computer designed in the mid-1980s, was a black cube with one side covered with a grid of red blinkenlights; the sales demo had them evolving Conway's Game of Life patterns.

The two CPU load monitors on the front of BeBoxes were also called "blinkenlights".

This word gave its name to several projects, including screen savers, hardware gadgets, and other nostalgic things. Some notable enterprises include the German Chaos Computer Club's Project Blinkenlights and the Blinkenlights Archaeological Institute.