Hardware Reference
In-Depth Information
Figure 18.17. Using a bent paperclip to jumper the adjacent green and black wires in the main
power connector to forcibly power on a system.
Caution
The continuous presence of the +5VSB power on pin 9 of the ATX main connector means the
motherboard is always receiving standby power from the power supply when connected to an
AC source, even when the computer is turned off. As a result, it is even more important to
unplug an ATX system from the power source before working inside the case than it is on
earlier model systems.
The remote switch on ATX and newer designs can only put the system in a soft-off state, in which the
system appears off but is still receiving standby power. Some ATX and newer power supplies
include a hard override AC power switch on the back, which essentially disconnects AC power from
the system when turned off. With the AC switch off, the system no longer receives standby power and
is essentially the same as being completely unplugged from an AC outlet.
Tip
The design of the ATX power switch is such that the motherboard actually controls the status
of the power supply. On systems with full support for ACPI, when you press the power switch,
the motherboard informs the OS to perform an orderly shutdown before the power is actually
turned off. However, if the system is locked up or corrupted, it can remain running when you
press the switch. In that situation, you can manually override the ACPI control by pressing the
switch continuously for more than 4 seconds, which overrides the software control and
forcibly turns off the system.
