[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; see also
scram switch.