Big red button
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A big red button (BRB), sometimes called a big red switch (BRS), is a real or fictional button with various functions. The purpose of being big and red is for its quick identification and actuation. In its more ominous forms, the phrases are often capitalized as the Big Red Button or the Big Red Switch.
- A shut-down switch for catastrophic circumstances to avert further damage or to cause it, e.g., an "emergency power-off" button.
- Help call in emergencies or for disabled persons.
- Firing or detonating a weapon, typically a nuclear device.
- In hacker jargon, the shutdown button or power switch on a computer, especially the red "emergency pull" switch on IBM mainframe operator consoles. The term has also sometimes been used for the power switch on IBM PCs.
On some mainframe designs, the emergency power-off switch would immediately physically disable the machine's power supply. Because the use of a Big Red Switch would bring down a computer in an uncontrolled fashion, getting the machine up and running again could be a nontrivial and time-consuming task. Therefore, particularly in the early mainframe computer era, people risked disciplinary action for activating the BRS of a production batch processing mainframe in a non-emergency situation (see molly-guard below).
During the 20th-century's Cold War, the "Big Red Button" (sometimes just "The Button") referred to a device used to launch nuclear weapons. A person in charge may be referred to as "having his/her finger on The Button". The disastrous consequences of a full-out nuclear war made the Big Red Button a symbol of the annihilation of humanity. In a real world case, Soviet lieutenant colonel Stanislav Petrov figuratively avoided pressing the Red Button by correctly identifying a missile attack warning as a false alarm.
Because of this potential doomsday use, Cold-War-era fiction often featured a BRB as the final trigger for a self-destruct process. It could also represent a "nuclear" or radical solution to a problem, much like "cutting the Gordian knot", and likely lead to the BRB's use as a reset button.
Once contemporary definitions of the BRB gained popularity as a plot device in Looney Tunes; the button became a running gag. A character would at some point be warned, "Whatever you do, do not press the red button." By the end of the cartoon someone would invariably press it, usually resulting in a large explosion. This attached a level of temptation to the button itself, and is often used in religious or philosophical allegory, a parallel to Adam and Eve's consumption of the forbidden fruit in the Garden of Eden. In his "MLF Lullaby," singer/satirist Tom Lehrer noted that development of a "Multi-Lateral (nuclear) Force" would ensure that "one of the fingers on the button will be German."
Computing and industrial 
An early "Big Red Switch" was on the mid Seventies IBM 5100 computer, it later appeared on the first 8088 (8086) IBM PCs. It was part of the PSU and located on the right side of the PC system unit, but on the front of the IBM 5100.
This switch was often located on the front of a personal computer or on the back next to the power supply. Most modern computer systems, however, either omit a reset button or significantly reduce its visibility and/or access to prevent users from accidentally triggering it. Although "hit the Big Red Switch" may still have a connotation of "reboot", current systems often have other means to accomplish this, like x86-based computers' Control-Alt-Delete key combination (sarcastically called the "three-finger salute" by frustrated users).
BRBs in IT or industrial settings are still used as kill switches, which cut all power to a device or a group of devices in an emergency, similar in use to a nuclear reactor's Scram Button. Data centers often have such kill switches near the entrance, and may release fire suppression systems as well.
A Big Red Switch often includes a molly-guard, a cover that must be lifted to trip the switch. The original molly-guard was jury-rigged from Plexiglas to prevent a programmer's young daughter Molly from pressing the BRS on an IBM 4341 server, after she had done so twice in one day.
Similarly, molly-guard is a package on Debian-based Linux distributions that traps shutdown and reboot commands over SSH, and confirms the machine is the correct machine by requiring the user to type the hostname of the system before the event will proceed. This helps prevent the user from inadvertently shutting down the wrong system.
See also 
- Clark, Laurence (4 November 2006). "The Big Red Button". Ouch!. BBC. Retrieved 2009-06-19.
- Finkel, Raphael; Don Woods, Mark Crispin, Guy Steele, Richard Stallman, Eric S. Raymond, et al. "Big Red Switch". Jargon File (version 4.4.7). Retrieved 2009-06-19.
- Finkel et al. "molly-guard". Jargon File (version 4.4.7). Retrieved 2009-06-19.
- "Debian -- Details of package molly-guard in sid". Retrieved 2010-03-08.