Big Red Switchn. [IBM] The power switch on a computer, esp. the `Emergency Pull' switch on an IBM mainframe or the power switch on an IBM PC where it really is large and red. "This !@%$% bitty box is hung again; time to hit the Big Red Switch." Sources at IBM report that, in tune with the company's passion for TLAs, this is often abbreviated as `BRS' (this has also become established on FidoNet and in the PC clone world). It is alleged that the emergency pull switch on an IBM 360/91 actually fired a non-conducting bolt into the main power feed; the BRSes on more recent mainframes physically drop a block into place so that they can't be pushed back in. People get fired for pulling them, especially inappropriately (see also molly-guard). Compare power cycle, three-finger salute, 120 reset; see also scram switch.