from
Jargon File (4.4.4, 14 Aug 2003)
Big Red Switch
n.
[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 !@%$% {bitty box} is hung again; time to hit
the Big Red Switch." Sources at IBM report that, in tune with the
company's passion for {TLA}s, this is often abbreviated as BRS (this
has also become established on FidoNet and in the PC {clone} world).
It is alleged that the emergency pull switch on an IBM 360/91 actually
fired a non-conducting bolt into the main power feed; the BRSes on
more recent mainframes physically drop a block into place so that they
can't be pushed back in. People get fired for pulling them, especially
inappropriately (see also {molly-guard}). Compare {power cycle},
{three-finger salute}; see also {scram switch}.
from
The Free On-line Dictionary of Computing (8 July 2008)
Big Red Switch
[IBM] The power switch on a computer, especially the
"Emergency Pull" switch on an IBM {mainframe} or the power
switch on an IBM PC where it really is large and red. "This
!@%$% {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
{IBM PC} 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}.