Big Red Switch

What Does Big Red Switch Mean?

The Big Red Switch (BRS) is a physical or metaphorical switch or button for which activation has ominous implications. A Big Red Switch is always very visible, and may stand as a warning itself as it is often designed to only be used in extreme situations. As such, the term has become a metaphor for extreme situations such that when an emgerency arises, someone might say “pull the Big Red Switch.”


Most often the Big Red Switch is a last resort in computer security, most specifically in mainframes or servers that have come under an attack that cannot be stopped and thus must be shut down. The term may also refer to major system resets.

The Big Red Switch may also be called the Big Red Button (BRB).

Techopedia Explains Big Red Switch

The emergency pull switch on old IBM mainframes were big and red, as was the power button on old IBM PCs. Oftentimes these buttons were used to prevent further catastrophe. However, the origins of the term may go even farther back, as the image of a red switch or button was widely used during the Cold War era, when nuclear missile launch buttons were often portrayed in this manner.

Literal Big Red Switches now have a “molly-guard”, which prevents accidental activation of the switch. It came to be known as such when the young daughter (Molly) of a programmer pulled the Big Red Switch, shutting down an IBM 4341 mainframe twice in a single day.


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Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.