Surge-Tolerant Power Supply; Thermal Sensor - Compaq Deskpro 4000N Reference Manual

Certain new Compaq monitors detect when the operating
temperature exceeds the normal range or when a hardware fault
occurs. Monitor hardware faults may include the following:
Power voltage out of range
Power current out of range
Horizontal deflection
Vertical deflection
I/O controller operation failure
If the monitor detects one of these conditions, the computer will
send an alert over the network to the system administrator.
An integrated, surge-tolerant power supply provides greater
reliability when the computer is hit with an unpredictable power
surge. This power supply is rated to withstand a power surge of
up to 2000 volts without incurring any system downtime or data
loss.
The thermal sensor is a hardware and software feature that
tracks the internal temperature of the computer. This feature
displays a warning message when the normal range is exceeded,
which gives you time to take action before internal components
are damaged or data is lost. If prompt action is not taken, the
system will shut down automatically to prevent damage to the
internal components. In this case, any unsaved data will be lost.